diff --git a/ShopIt_API_Postman_Collection.json b/ShopIt_API_Postman_Collection.json
index 50301a5..8be9135 100644
--- a/ShopIt_API_Postman_Collection.json
+++ b/ShopIt_API_Postman_Collection.json
@@ -1155,7 +1155,7 @@
                             "response": []
                         },
                         {
-                            "name": "Update Item Quantity Purchase",
+                            "name": "Update Item Purchase",
                             "request": {
                                 "method": "PATCH",
                                 "header": [
@@ -1170,7 +1170,7 @@
                                         "type": "text"
                                     }
                                 ],
-                                "description": "Ruta Laravel: `PATCH /api/tenants/{tenant:codigo}/compras/{compra}/items/{item}`\n\nControlador: `App\\Domains\\Purchase\\Controllers\\PurchaseController@updateItemQuantity`\n\nRequiere autenticación Sanctum.",
+                                "description": "Ruta Laravel: `PATCH /api/tenants/{tenant:codigo}/compras/{compra}/items/{item}`\n\nControlador: `App\\Domains\\Purchase\\Controllers\\PurchaseController@updateItem`\n\nRequiere autenticación Sanctum.",
                                 "url": {
                                     "raw": "{{base_url}}/api/tenants/{{tenant_code}}/compras/{{purchase_id}}/items/{{purchase_item_id}}",
                                     "host": [
@@ -1188,7 +1188,7 @@
                                 },
                                 "body": {
                                     "mode": "raw",
-                                    "raw": "{\n    \"quantity\": 2\n}",
+                                    "raw": "{\n    \"quantity\": 2,\n    \"variant_id\": {{variant_id}}\n}",
                                     "options": {
                                         "raw": {
                                             "language": "json"
diff --git a/app/Domains/Purchase/Controllers/PurchaseController.php b/app/Domains/Purchase/Controllers/PurchaseController.php
index 5439563..32e6830 100644
--- a/app/Domains/Purchase/Controllers/PurchaseController.php
+++ b/app/Domains/Purchase/Controllers/PurchaseController.php
@@ -8,8 +8,9 @@ use App\Domains\Purchase\Models\PurchaseItem;
 use App\Domains\Purchase\Requests\PaymentIntentRequest;
 use App\Domains\Purchase\Requests\StartCheckoutRequest;
 use App\Domains\Purchase\Requests\UpdatePurchaseCustomerRequest;
-use App\Domains\Purchase\Requests\UpdatePurchaseItemQuantityRequest;
+use App\Domains\Purchase\Requests\UpdatePurchaseItemRequest;
 use App\Domains\Purchase\Resources\PurchaseResource;
+use App\Domains\Purchase\Services\Checkout\PurchaseResponseLoader;
 use App\Domains\Purchase\Services\CheckoutService;
 use App\Domains\Tenant\Models\Tenant;
 use App\Http\Controllers\Controller;
@@ -52,12 +53,16 @@ class PurchaseController extends Controller
         return PurchaseResource::make($purchase)->response()->setStatusCode(201);
     }
 
-    public function show(Request $request, Tenant $tenant, Purchase $compra): PurchaseResource
-    {
+    public function show(
+        Request $request,
+        Tenant $tenant,
+        Purchase $compra,
+        PurchaseResponseLoader $responses,
+    ): PurchaseResource {
         $compra = $this->resolveScopedPurchase($tenant, $request->user()->id, $compra);
 
         $compra->loadMissing('items')->loadCount('tickets');
-        $compra->items->load('imageAttachment');
+        $responses->load($compra);
 
         return PurchaseResource::make($compra);
     }
@@ -75,8 +80,8 @@ class PurchaseController extends Controller
         );
     }
 
-    public function updateItemQuantity(
-        UpdatePurchaseItemQuantityRequest $request,
+    public function updateItem(
+        UpdatePurchaseItemRequest $request,
         Tenant $tenant,
         Purchase $compra,
         PurchaseItem $item,
@@ -85,10 +90,12 @@ class PurchaseController extends Controller
         $compra = $this->resolveScopedPurchase($tenant, $request->user()->id, $compra);
 
         return PurchaseResource::make(
-            $checkoutService->updateItemQuantity(
+            $checkoutService->updateItem(
                 $compra,
                 $item,
-                (int) $request->validated('quantity'),
+                $request->exists('quantity') ? (int) $request->validated('quantity') : null,
+                $request->exists('variant_id') ? (int) $request->validated('variant_id') : null,
+                $request->exists('variant_id'),
             ),
         );
     }
diff --git a/app/Domains/Purchase/Models/PurchaseItem.php b/app/Domains/Purchase/Models/PurchaseItem.php
index 7f82f2c..9a970ed 100644
--- a/app/Domains/Purchase/Models/PurchaseItem.php
+++ b/app/Domains/Purchase/Models/PurchaseItem.php
@@ -3,6 +3,8 @@
 namespace App\Domains\Purchase\Models;
 
 use App\Domains\Attachable\Models\Attachment;
+use App\Domains\Catalog\Models\CatalogItem;
+use App\Domains\Catalog\Models\Variant;
 use Illuminate\Database\Eloquent\Attributes\Fillable;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
@@ -66,4 +68,16 @@ class PurchaseItem extends Model
     {
         return $this->belongsTo(Attachment::class, 'image_attachment_id');
     }
+
+    /** @return BelongsTo<CatalogItem, $this> */
+    public function sourceCatalogItem(): BelongsTo
+    {
+        return $this->belongsTo(CatalogItem::class, 'source_catalog_item_id')->withTrashed();
+    }
+
+    /** @return BelongsTo<Variant, $this> */
+    public function sourceVariant(): BelongsTo
+    {
+        return $this->belongsTo(Variant::class, 'source_variant_id')->withTrashed();
+    }
 }
diff --git a/app/Domains/Purchase/Requests/UpdatePurchaseItemQuantityRequest.php b/app/Domains/Purchase/Requests/UpdatePurchaseItemQuantityRequest.php
deleted file mode 100644
index 9810352..0000000
--- a/app/Domains/Purchase/Requests/UpdatePurchaseItemQuantityRequest.php
+++ /dev/null
@@ -1,23 +0,0 @@
-<?php
-
-namespace App\Domains\Purchase\Requests;
-
-use Illuminate\Foundation\Http\FormRequest;
-
-class UpdatePurchaseItemQuantityRequest extends FormRequest
-{
-    public function authorize(): bool
-    {
-        return $this->user() !== null;
-    }
-
-    /**
-     * @return array<string, mixed>
-     */
-    public function rules(): array
-    {
-        return [
-            'quantity' => ['required', 'integer', 'min:1', 'max:100'],
-        ];
-    }
-}
diff --git a/app/Domains/Purchase/Requests/UpdatePurchaseItemRequest.php b/app/Domains/Purchase/Requests/UpdatePurchaseItemRequest.php
new file mode 100644
index 0000000..ba05e14
--- /dev/null
+++ b/app/Domains/Purchase/Requests/UpdatePurchaseItemRequest.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace App\Domains\Purchase\Requests;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class UpdatePurchaseItemRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return $this->user() !== null;
+    }
+
+    /** @return array<string, mixed> */
+    public function rules(): array
+    {
+        return [
+            'quantity' => ['sometimes', 'required_without:variant_id', 'integer', 'min:1', 'max:100'],
+            'variant_id' => ['sometimes', 'required_without:quantity', 'integer', 'min:1'],
+        ];
+    }
+}
diff --git a/app/Domains/Purchase/Resources/PurchaseItemResource.php b/app/Domains/Purchase/Resources/PurchaseItemResource.php
index 5fb2b90..c91e62b 100644
--- a/app/Domains/Purchase/Resources/PurchaseItemResource.php
+++ b/app/Domains/Purchase/Resources/PurchaseItemResource.php
@@ -3,6 +3,7 @@
 namespace App\Domains\Purchase\Resources;
 
 use App\Domains\Cart\Models\CartItem;
+use App\Domains\Catalog\Enums\InventoryPolicy;
 use App\Domains\Catalog\Models\CatalogItem;
 use App\Domains\Catalog\Models\Variant;
 use App\Domains\Purchase\Models\PurchaseItem;
@@ -25,6 +26,14 @@ class PurchaseItemResource extends JsonResource
                 : null;
             $attributes = $this->variant_attributes ?? [];
 
+            $catalogItem = $this->relationLoaded('sourceCatalogItem')
+                ? $this->sourceCatalogItem
+                : null;
+            $includeVariants = $tenant instanceof Tenant
+                && $tenant->cart_editing_policy->allowsVariantChanges()
+                && $catalogItem !== null
+                && $catalogItem->relationLoaded('variants');
+
             return [
                 'id' => $this->id,
                 'quantity' => (int) $this->cantidad,
@@ -39,6 +48,13 @@ class PurchaseItemResource extends JsonResource
                     'imagen' => $imageUrl,
                     'attributes' => $attributes,
                 ],
+                'variants' => $this->when(
+                    $includeVariants,
+                    fn () => $catalogItem
+                        ->visibleVariants($this->source_variant_id)
+                        ->map(fn (Variant $variant): array => $this->variantData($catalogItem, $variant))
+                        ->values(),
+                ),
             ];
         }
 
@@ -142,4 +158,17 @@ class PurchaseItemResource extends JsonResource
     {
         return number_format((float) ($amount ?? 0), 2, '.', '');
     }
+
+    /** @return array<string, mixed> */
+    private function variantData(CatalogItem $catalogItem, Variant $variant): array
+    {
+        return [
+            'id' => $variant->id,
+            'precio' => $this->formatMoney($variant->precio ?? $catalogItem->precio),
+            'stock_tecnico' => $catalogItem->inventory_policy === InventoryPolicy::Unlimited
+                ? null
+                : $variant->inventory->availableStock(),
+            'values' => $variant->selectorOptions($catalogItem->itemAttributes),
+        ];
+    }
 }
diff --git a/app/Domains/Purchase/Services/Checkout/EditCheckoutService.php b/app/Domains/Purchase/Services/Checkout/EditCheckoutService.php
index 9491b38..6178673 100644
--- a/app/Domains/Purchase/Services/Checkout/EditCheckoutService.php
+++ b/app/Domains/Purchase/Services/Checkout/EditCheckoutService.php
@@ -18,6 +18,8 @@ class EditCheckoutService
         private readonly UserPurchaseLimitService $purchaseLimits,
         private readonly CatalogSelectionResolver $selections,
         private readonly SourceCartService $sourceCart,
+        private readonly PurchaseItemSnapshotFactory $snapshots,
+        private readonly PurchaseResponseLoader $responses,
     ) {}
 
     /** @param array<string, string> $customerData */
@@ -33,12 +35,20 @@ class EditCheckoutService
         });
     }
 
-    public function updateItemQuantity(
+    public function updateItem(
         Purchase $purchase,
         PurchaseItem $purchaseItem,
-        int $quantity,
+        ?int $quantity,
+        ?int $variantId,
+        bool $updateVariant,
     ): Purchase {
-        return DB::transaction(function () use ($purchase, $purchaseItem, $quantity): Purchase {
+        return DB::transaction(function () use (
+            $purchase,
+            $purchaseItem,
+            $quantity,
+            $variantId,
+            $updateVariant,
+        ): Purchase {
             $purchase = $this->lockPurchase($purchase);
 
             if ($purchase->status !== Purchase::STATUS_CREATED || $this->hasExpired($purchase)) {
@@ -48,16 +58,40 @@ class EditCheckoutService
             }
 
             $purchaseItem = $this->lockPurchaseItem($purchase, $purchaseItem);
-            $difference = $quantity - (int) $purchaseItem->cantidad;
+            $tenant = $purchase->tenant()->firstOrFail();
+            $finalQuantity = $quantity ?? (int) $purchaseItem->cantidad;
 
-            if ($difference !== 0) {
-                $this->adjustReservation($purchase, $purchaseItem, $quantity, $difference);
-
-                $purchaseItem->update([
-                    'cantidad' => $quantity,
-                    'total' => (float) $purchaseItem->precio_unitario * $quantity,
+            if ($quantity !== null && ! $tenant->cart_editing_policy->allowsQuantityChanges()) {
+                throw ValidationException::withMessages([
+                    'quantity' => __('api.cart.editing_disabled'),
                 ]);
-                $this->sourceCart->syncItemQuantity($purchase, $purchaseItem, $quantity);
+            }
+
+            if ($updateVariant && ! $tenant->cart_editing_policy->allowsVariantChanges()) {
+                throw ValidationException::withMessages([
+                    'variant_id' => __('api.purchase.variant_change_disabled'),
+                ]);
+            }
+
+            if ($updateVariant && $variantId !== $purchaseItem->source_variant_id) {
+                $this->changeItemVariant(
+                    $purchase,
+                    $purchaseItem,
+                    (int) $variantId,
+                    $finalQuantity,
+                );
+            } else {
+                $difference = $finalQuantity - (int) $purchaseItem->cantidad;
+
+                if ($difference !== 0) {
+                    $this->adjustReservation($purchase, $purchaseItem, $finalQuantity, $difference);
+
+                    $purchaseItem->update([
+                        'cantidad' => $finalQuantity,
+                        'total' => (float) $purchaseItem->precio_unitario * $finalQuantity,
+                    ]);
+                    $this->sourceCart->syncItemQuantity($purchase, $purchaseItem, $finalQuantity);
+                }
             }
 
             $purchase->update([
@@ -68,12 +102,94 @@ class EditCheckoutService
         });
     }
 
+    private function changeItemVariant(
+        Purchase $purchase,
+        PurchaseItem $sourceItem,
+        int $variantId,
+        int $quantity,
+    ): void {
+        $tenant = $purchase->tenant()->firstOrFail();
+        $currentSelection = $this->selections->resolvePurchaseItem($tenant, $sourceItem);
+        $targetSelection = $this->selections->resolve(
+            $tenant,
+            (int) $sourceItem->source_catalog_item_id,
+            $variantId,
+            'item',
+        );
+
+        if (! $targetSelection instanceof Variant) {
+            throw ValidationException::withMessages([
+                'variant_id' => __('api.cart.variant_required'),
+            ]);
+        }
+
+        /** @var PurchaseItem|null $targetItem */
+        $targetItem = $purchase->items()
+            ->where('source_catalog_item_id', $sourceItem->source_catalog_item_id)
+            ->where('source_variant_id', $targetSelection->id)
+            ->whereKeyNot($sourceItem->getKey())
+            ->lockForUpdate()
+            ->first();
+
+        if ($targetItem !== null && $targetItem->reservation_status !== PurchaseItem::RESERVATION_ACTIVE) {
+            throw ValidationException::withMessages([
+                'variant_id' => __('api.purchase.item_not_editable'),
+            ]);
+        }
+
+        $otherItemQuantity = (int) $purchase->items()
+            ->where('source_catalog_item_id', $sourceItem->source_catalog_item_id)
+            ->whereKeyNot($sourceItem->getKey())
+            ->sum('cantidad');
+        $this->purchaseLimits->assertCanPurchase(
+            $targetSelection->catalogItem,
+            (int) $purchase->user_id,
+            $otherItemQuantity + $quantity,
+            $purchase->getKey(),
+            'variant_id',
+        );
+
+        try {
+            $this->inventory->release($currentSelection, (int) $sourceItem->cantidad);
+            $this->inventory->reserve($targetSelection, $quantity);
+        } catch (\InvalidArgumentException) {
+            throw ValidationException::withMessages([
+                'variant_id' => __('api.purchase.insufficient_stock'),
+            ]);
+        }
+
+        $previousVariantId = $sourceItem->source_variant_id;
+        $finalQuantity = $quantity;
+
+        if ($targetItem !== null) {
+            $finalQuantity += (int) $targetItem->cantidad;
+            $targetItem->update($this->snapshots->fromVariant($targetSelection, $finalQuantity));
+            $sourceItem->delete();
+        } else {
+            $sourceItem->update($this->snapshots->fromVariant($targetSelection, $finalQuantity));
+        }
+
+        $this->sourceCart->syncItemSelection(
+            $purchase,
+            (int) $sourceItem->source_catalog_item_id,
+            $previousVariantId,
+            $targetSelection->id,
+            $finalQuantity,
+        );
+    }
+
     public function prepareItemEditing(Purchase $purchase): Purchase
     {
         return DB::transaction(function () use ($purchase): Purchase {
             $purchase = $this->lockPurchase($purchase);
             $this->assertEditable($purchase);
 
+            if (! $purchase->tenant()->firstOrFail()->cart_editing_policy->allowsModification()) {
+                throw ValidationException::withMessages([
+                    'purchase' => __('api.cart.editing_disabled'),
+                ]);
+            }
+
             $purchase->telepagosQr()->delete();
             $purchase->update([
                 'status' => Purchase::STATUS_CREATED,
@@ -170,6 +286,6 @@ class EditCheckoutService
 
     private function loadPurchase(Purchase $purchase): Purchase
     {
-        return $purchase->load(['items.imageAttachment']);
+        return $this->responses->load($purchase);
     }
 }
diff --git a/app/Domains/Purchase/Services/Checkout/PurchaseItemSnapshotFactory.php b/app/Domains/Purchase/Services/Checkout/PurchaseItemSnapshotFactory.php
index e1711a2..c791820 100644
--- a/app/Domains/Purchase/Services/Checkout/PurchaseItemSnapshotFactory.php
+++ b/app/Domains/Purchase/Services/Checkout/PurchaseItemSnapshotFactory.php
@@ -10,6 +10,35 @@ use Illuminate\Support\Collection;
 
 class PurchaseItemSnapshotFactory
 {
+    /** @return array<string, mixed> */
+    public function fromVariant(Variant $variant, int $quantity): array
+    {
+        $variant->loadMissing([
+            'attachments',
+            'catalogItem.attachments',
+            'definitions.itemAttribute.attribute.options',
+            'eventDates',
+            'eventDate',
+        ]);
+        $unitPrice = $variant->getPrice();
+
+        return [
+            'source_variant_id' => $variant->id,
+            'image_attachment_id' => $variant->attachments->first()?->id
+                ?? $variant->catalogItem->attachments->first()?->id,
+            'nombre' => $variant->catalogItem->nombre,
+            'descripcion' => $variant->getDescription(),
+            'slug' => $variant->catalogItem->slug,
+            'item_nombre' => $variant->getName(),
+            'variant_attributes' => $this->snapshotAttributes($variant),
+            'cantidad' => $quantity,
+            'precio_unitario' => $unitPrice,
+            'discount_total' => null,
+            'tax_total' => null,
+            'total' => $unitPrice * $quantity,
+        ];
+    }
+
     /**
      * @param  Collection<int, CartItem>  $cartItems
      * @return array<int, array<string, mixed>>
diff --git a/app/Domains/Purchase/Services/Checkout/PurchaseResponseLoader.php b/app/Domains/Purchase/Services/Checkout/PurchaseResponseLoader.php
new file mode 100644
index 0000000..f9dd775
--- /dev/null
+++ b/app/Domains/Purchase/Services/Checkout/PurchaseResponseLoader.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Domains\Purchase\Services\Checkout;
+
+use App\Domains\Purchase\Models\Purchase;
+
+class PurchaseResponseLoader
+{
+    public function load(Purchase $purchase): Purchase
+    {
+        $purchase->load(['tenant', 'items.imageAttachment']);
+
+        if (! $purchase->tenant->cart_editing_policy->allowsVariantChanges()) {
+            return $purchase;
+        }
+
+        $purchase->load([
+            'items.sourceCatalogItem.itemAttributes.attribute',
+            'items.sourceCatalogItem.variants' => fn ($query) => $query->orderBy('id'),
+            'items.sourceCatalogItem.variants.inventory',
+            'items.sourceCatalogItem.variants.definitions' => fn ($query) => $query->orderBy('id'),
+            'items.sourceCatalogItem.variants.definitions.itemAttribute.attribute.options',
+            'items.sourceCatalogItem.variants.eventDates',
+            'items.sourceCatalogItem.variants.eventDate',
+        ]);
+
+        return $purchase;
+    }
+}
diff --git a/app/Domains/Purchase/Services/Checkout/SourceCartService.php b/app/Domains/Purchase/Services/Checkout/SourceCartService.php
index 45624cd..3184aad 100644
--- a/app/Domains/Purchase/Services/Checkout/SourceCartService.php
+++ b/app/Domains/Purchase/Services/Checkout/SourceCartService.php
@@ -71,6 +71,57 @@ class SourceCartService
             ->update(['cantidad' => $quantity]);
     }
 
+    public function syncItemSelection(
+        Purchase $purchase,
+        int $catalogItemId,
+        ?int $previousVariantId,
+        int $newVariantId,
+        int $finalQuantity,
+    ): void {
+        $sourceCart = $this->findSourceCart($purchase);
+
+        if ($sourceCart === null) {
+            return;
+        }
+
+        /** @var CartItem|null $previousItem */
+        $previousItem = $sourceCart->items()
+            ->where('catalog_item_id', $catalogItemId)
+            ->where('variant_id', $previousVariantId)
+            ->lockForUpdate()
+            ->first();
+
+        /** @var CartItem|null $targetItem */
+        $targetItem = $sourceCart->items()
+            ->where('catalog_item_id', $catalogItemId)
+            ->where('variant_id', $newVariantId)
+            ->when($previousItem !== null, fn ($query) => $query->whereKeyNot($previousItem->getKey()))
+            ->lockForUpdate()
+            ->first();
+
+        if ($targetItem !== null) {
+            $targetItem->update(['cantidad' => $finalQuantity]);
+            $previousItem?->delete();
+
+            return;
+        }
+
+        if ($previousItem !== null) {
+            $previousItem->update([
+                'variant_id' => $newVariantId,
+                'cantidad' => $finalQuantity,
+            ]);
+
+            return;
+        }
+
+        $sourceCart->items()->create([
+            'catalog_item_id' => $catalogItemId,
+            'variant_id' => $newVariantId,
+            'cantidad' => $finalQuantity,
+        ]);
+    }
+
     public function finalize(Purchase $purchase): void
     {
         $sourceCart = $this->findSourceCart($purchase);
diff --git a/app/Domains/Purchase/Services/Checkout/StartCheckoutService.php b/app/Domains/Purchase/Services/Checkout/StartCheckoutService.php
index 60a7ccb..6f0bff9 100644
--- a/app/Domains/Purchase/Services/Checkout/StartCheckoutService.php
+++ b/app/Domains/Purchase/Services/Checkout/StartCheckoutService.php
@@ -24,6 +24,7 @@ class StartCheckoutService
         private readonly CatalogSelectionResolver $selections,
         private readonly PurchaseItemSnapshotFactory $snapshots,
         private readonly InsufficientStockMessageBuilder $stockMessages,
+        private readonly PurchaseResponseLoader $responses,
     ) {}
 
     /** @param array<string, mixed> $purchaseData */
@@ -382,6 +383,6 @@ class StartCheckoutService
 
     private function loadPurchase(Purchase $purchase): Purchase
     {
-        return $purchase->load(['items.imageAttachment']);
+        return $this->responses->load($purchase);
     }
 }
diff --git a/app/Domains/Purchase/Services/CheckoutService.php b/app/Domains/Purchase/Services/CheckoutService.php
index b575acd..c87ca99 100644
--- a/app/Domains/Purchase/Services/CheckoutService.php
+++ b/app/Domains/Purchase/Services/CheckoutService.php
@@ -47,12 +47,20 @@ class CheckoutService
         return $this->editor->updateCustomer($purchase, $customerData);
     }
 
-    public function updateItemQuantity(
+    public function updateItem(
         Purchase $purchase,
         PurchaseItem $purchaseItem,
-        int $quantity,
+        ?int $quantity,
+        ?int $variantId,
+        bool $updateVariant,
     ): Purchase {
-        return $this->editor->updateItemQuantity($purchase, $purchaseItem, $quantity);
+        return $this->editor->updateItem(
+            $purchase,
+            $purchaseItem,
+            $quantity,
+            $variantId,
+            $updateVariant,
+        );
     }
 
     public function prepareItemEditing(Purchase $purchase): Purchase
diff --git a/app/Domains/Purchase/routes/api.php b/app/Domains/Purchase/routes/api.php
index 41cc919..2fb537e 100644
--- a/app/Domains/Purchase/routes/api.php
+++ b/app/Domains/Purchase/routes/api.php
@@ -8,7 +8,7 @@ Route::prefix('tenants/{tenant:codigo}')->middleware('auth:sanctum')->group(func
     Route::post('compras/start-checkout', [PurchaseController::class, 'startCheckout']);
     Route::get('compras/{compra}', [PurchaseController::class, 'show']);
     Route::post('compras/{compra}/edit-items', [PurchaseController::class, 'prepareItemEditing']);
-    Route::patch('compras/{compra}/items/{item}', [PurchaseController::class, 'updateItemQuantity']);
+    Route::patch('compras/{compra}/items/{item}', [PurchaseController::class, 'updateItem']);
     Route::patch('compras/{compra}/customer-data', [PurchaseController::class, 'updateCustomerData']);
     Route::post('compras/{compra}/payment-intent', [PurchaseController::class, 'paymentIntent']);
     Route::post('compras/{compra}/complete', [PurchaseController::class, 'complete']);
diff --git a/lang/en/api.php b/lang/en/api.php
index 89a12c0..4a9ebf0 100644
--- a/lang/en/api.php
+++ b/lang/en/api.php
@@ -36,6 +36,7 @@ return [
         'variant_required' => 'You must select a variant for this item.',
     ],
     'purchase' => [
+        'variant_change_disabled' => 'Variant changes are disabled for this purchase.',
         'source_required' => 'A cart or direct item is required.',
         'payment_method_required' => 'The purchase payment method must be selected before finalizing.',
         'not_editable' => 'The purchase is no longer editable.',
diff --git a/lang/es/api.php b/lang/es/api.php
index 53b2911..0008179 100644
--- a/lang/es/api.php
+++ b/lang/es/api.php
@@ -36,6 +36,7 @@ return [
         'variant_required' => 'Debe seleccionar una variante para este ítem.',
     ],
     'purchase' => [
+        'variant_change_disabled' => 'El cambio de variante está deshabilitado para esta compra.',
         'source_required' => 'Se requiere un carrito o un producto directo.',
         'payment_method_required' => 'Debes seleccionar el método de pago antes de finalizar la compra.',
         'not_editable' => 'La compra ya no se puede modificar.',
diff --git a/postman/generate-shopit-collection.php b/postman/generate-shopit-collection.php
index 1fc99f9..2e7e31b 100644
--- a/postman/generate-shopit-collection.php
+++ b/postman/generate-shopit-collection.php
@@ -84,7 +84,7 @@ function bodyFor(string $method, string $uri): ?array
         'POST api/tenants/{tenant:codigo}/catalog-items/{catalogItem}/variant-options' => ['selected_values' => ['color' => 'azul'], 'cart_item_id' => '{{cart_item_id}}'],
         'POST api/tenants/{tenant:codigo}/compras/start-checkout' => ['cart_id' => '{{cart_id}}'],
         'PATCH api/tenants/{tenant:codigo}/compras/{compra}/customer-data' => ['dni' => '30123456', 'telefono' => '+5491112345678', 'nombre_apellido' => 'Usuario Demo', 'email' => '{{user_email}}'],
-        'PATCH api/tenants/{tenant:codigo}/compras/{compra}/items/{item}' => ['quantity' => 2],
+        'PATCH api/tenants/{tenant:codigo}/compras/{compra}/items/{item}' => ['quantity' => 2, 'variant_id' => '{{variant_id}}'],
         'POST api/tenants/{tenant:codigo}/compras/{compra}/payment-intent' => ['method' => 'transfer', 'transfer_payer_dni' => '30123456'],
         'POST api/tenants/{tenant:codigo}/tickets/pdf' => ['ticket_ids' => [1]],
         'POST api/v1/adminapp/login' => ['email' => '{{admin_email}}', 'password' => '{{admin_password}}'],
@@ -244,6 +244,7 @@ function requestName(string $method, string $action, bool $multiMethod): string
     $verbs = [
         'index' => 'List', 'store' => 'Create', 'show' => 'Get', 'update' => 'Update',
         'destroy' => 'Delete', 'addItem' => 'Add Item', 'updateItemQuantity' => 'Update Item Quantity',
+        'updateItem' => 'Update Item',
         'removeItem' => 'Remove Item', 'search' => 'Search', 'category' => 'Get Category',
         'featuredGroupItems' => 'List Featured Group Items', 'variantOptions' => 'Get Variant Options',
         'startCheckout' => 'Start Checkout', 'updateCustomerData' => 'Update Customer Data',
diff --git a/tests/Feature/Purchase/StorePurchaseTest.php b/tests/Feature/Purchase/StorePurchaseTest.php
index 601567a..ecb83d5 100644
--- a/tests/Feature/Purchase/StorePurchaseTest.php
+++ b/tests/Feature/Purchase/StorePurchaseTest.php
@@ -580,6 +580,182 @@ class StorePurchaseTest extends TestCase
         ]);
     }
 
+    public function test_it_changes_a_checkout_item_variant_and_moves_its_reservation(): void
+    {
+        $tenant = $this->createTenant('sonder', 'Sonder', 'sonder.com.ar');
+        $tenant->update(['cart_editing_policy' => 'full']);
+        $user = User::factory()->create();
+        $firstVariant = $this->createVariantForTenant('sonder', 10, '50.00');
+        $secondInventory = Inventory::query()->create(['real_stock' => 10]);
+        $secondVariant = $firstVariant->catalogItem->variants()->create([
+            'inventory_id' => $secondInventory->id,
+            'precio' => '70.00',
+        ]);
+        $purchase = $this->createCheckoutPurchase($user, 'sonder', $firstVariant, 2);
+        $itemId = $purchase->items->firstOrFail()->id;
+
+        $this->actingAs($user, 'sanctum')
+            ->patchJson("/api/tenants/sonder/compras/{$purchase->id}/items/{$itemId}", [
+                'variant_id' => $secondVariant->id,
+            ])
+            ->assertOk()
+            ->assertJsonPath('data.items.0.source_variant_id', $secondVariant->id)
+            ->assertJsonPath('data.items.0.quantity', 2)
+            ->assertJsonPath('data.items.0.unit_price', '70.00')
+            ->assertJsonPath('data.items.0.line_total', '140.00')
+            ->assertJsonPath('data.total', '140.00')
+            ->assertJsonPath('data.items.0.variants.0.id', $firstVariant->id)
+            ->assertJsonPath('data.items.0.variants.1.id', $secondVariant->id);
+
+        $this->assertDatabaseHas('inventories', [
+            'id' => $firstVariant->inventory_id,
+            'reserved_stock' => 0,
+        ]);
+        $this->assertDatabaseHas('inventories', [
+            'id' => $secondInventory->id,
+            'reserved_stock' => 2,
+        ]);
+        $this->assertDatabaseHas('carrito_items', [
+            'cart_id' => $purchase->cart_id,
+            'catalog_item_id' => $firstVariant->catalog_item_id,
+            'variant_id' => $secondVariant->id,
+            'cantidad' => 2,
+        ]);
+        $this->assertDatabaseMissing('carrito_items', [
+            'cart_id' => $purchase->cart_id,
+            'variant_id' => $firstVariant->id,
+        ]);
+    }
+
+    public function test_it_rejects_checkout_variant_changes_when_the_policy_does_not_allow_them(): void
+    {
+        $tenant = $this->createTenant('sonder', 'Sonder', 'sonder.com.ar');
+        $tenant->update(['cart_editing_policy' => 'quantity_and_remove']);
+        $user = User::factory()->create();
+        $firstVariant = $this->createVariantForTenant('sonder', 10, '50.00');
+        $secondInventory = Inventory::query()->create(['real_stock' => 10]);
+        $secondVariant = $firstVariant->catalogItem->variants()->create([
+            'inventory_id' => $secondInventory->id,
+        ]);
+        $purchase = $this->createCheckoutPurchase($user, 'sonder', $firstVariant, 2);
+        $itemId = $purchase->items->firstOrFail()->id;
+
+        $this->actingAs($user, 'sanctum')
+            ->patchJson("/api/tenants/sonder/compras/{$purchase->id}/items/{$itemId}", [
+                'variant_id' => $secondVariant->id,
+            ])
+            ->assertUnprocessable()
+            ->assertJsonValidationErrors('variant_id');
+
+        $this->assertDatabaseHas('compra_items', [
+            'id' => $itemId,
+            'source_variant_id' => $firstVariant->id,
+            'cantidad' => 2,
+        ]);
+        $this->assertDatabaseHas('inventories', [
+            'id' => $firstVariant->inventory_id,
+            'reserved_stock' => 2,
+        ]);
+        $this->assertDatabaseHas('inventories', [
+            'id' => $secondInventory->id,
+            'reserved_stock' => 0,
+        ]);
+    }
+
+    public function test_checkout_variant_change_rolls_back_when_the_target_has_insufficient_stock(): void
+    {
+        $tenant = $this->createTenant('sonder', 'Sonder', 'sonder.com.ar');
+        $tenant->update(['cart_editing_policy' => 'full']);
+        $user = User::factory()->create();
+        $firstVariant = $this->createVariantForTenant('sonder', 10, '50.00');
+        $secondInventory = Inventory::query()->create(['real_stock' => 1]);
+        $secondVariant = $firstVariant->catalogItem->variants()->create([
+            'inventory_id' => $secondInventory->id,
+            'precio' => '70.00',
+        ]);
+        $purchase = $this->createCheckoutPurchase($user, 'sonder', $firstVariant, 2);
+        $itemId = $purchase->items->firstOrFail()->id;
+
+        $this->actingAs($user, 'sanctum')
+            ->patchJson("/api/tenants/sonder/compras/{$purchase->id}/items/{$itemId}", [
+                'variant_id' => $secondVariant->id,
+            ])
+            ->assertUnprocessable()
+            ->assertJsonValidationErrors('variant_id');
+
+        $this->assertDatabaseHas('compra_items', [
+            'id' => $itemId,
+            'source_variant_id' => $firstVariant->id,
+            'cantidad' => 2,
+            'precio_unitario' => '50.00',
+        ]);
+        $this->assertDatabaseHas('inventories', [
+            'id' => $firstVariant->inventory_id,
+            'reserved_stock' => 2,
+        ]);
+        $this->assertDatabaseHas('inventories', [
+            'id' => $secondInventory->id,
+            'reserved_stock' => 0,
+        ]);
+        $this->assertDatabaseHas('carrito_items', [
+            'cart_id' => $purchase->cart_id,
+            'variant_id' => $firstVariant->id,
+            'cantidad' => 2,
+        ]);
+    }
+
+    public function test_changing_to_an_existing_checkout_variant_merges_purchase_and_cart_rows(): void
+    {
+        $tenant = $this->createTenant('sonder', 'Sonder', 'sonder.com.ar');
+        $tenant->update(['cart_editing_policy' => 'full']);
+        $user = User::factory()->create();
+        $firstVariant = $this->createVariantForTenant('sonder', 10, '50.00');
+        $secondInventory = Inventory::query()->create(['real_stock' => 10]);
+        $secondVariant = $firstVariant->catalogItem->variants()->create([
+            'inventory_id' => $secondInventory->id,
+            'precio' => '70.00',
+        ]);
+        $cart = Cart::query()->create([
+            'tenant_codigo' => 'sonder',
+            'user_id' => $user->id,
+            'status' => 'active',
+        ]);
+        $cart->addItem($firstVariant->catalog_item_id, $firstVariant->id, 2);
+        $cart->addItem($secondVariant->catalog_item_id, $secondVariant->id, 3);
+        $purchase = app(CheckoutService::class)->startCheckout($tenant, $user->id, [
+            'cart_id' => $cart->id,
+        ]);
+        $sourceItem = $purchase->items->firstWhere('source_variant_id', $firstVariant->id);
+        $this->assertNotNull($sourceItem);
+
+        $this->actingAs($user, 'sanctum')
+            ->patchJson("/api/tenants/sonder/compras/{$purchase->id}/items/{$sourceItem->id}", [
+                'variant_id' => $secondVariant->id,
+            ])
+            ->assertOk()
+            ->assertJsonCount(1, 'data.items')
+            ->assertJsonPath('data.items.0.source_variant_id', $secondVariant->id)
+            ->assertJsonPath('data.items.0.quantity', 5)
+            ->assertJsonPath('data.items.0.line_total', '350.00')
+            ->assertJsonPath('data.total', '350.00');
+
+        $this->assertDatabaseCount('compra_items', 1);
+        $this->assertDatabaseHas('inventories', [
+            'id' => $firstVariant->inventory_id,
+            'reserved_stock' => 0,
+        ]);
+        $this->assertDatabaseHas('inventories', [
+            'id' => $secondInventory->id,
+            'reserved_stock' => 5,
+        ]);
+        $this->assertDatabaseCount('carrito_items', 1);
+        $this->assertDatabaseHas('carrito_items', [
+            'cart_id' => $cart->id,
+            'variant_id' => $secondVariant->id,
+            'cantidad' => 5,
+        ]);
+    }
+
     public function test_it_rejects_a_quantity_update_above_the_user_purchase_limit(): void
     {
         $this->createTenant('sonder', 'Sonder', 'sonder.com.ar');