Unfortunately, you cannot delete a received PO because it is tied to your inventory. However, you can have it "removed" from your Open Purchase Order list by following these steps:
- Go to Inventory > Inventory and Value.
 - Search for the inventory item listed on the purchase order.
 - Open the inventory item details page.
 - Under the "Transactions" section, add a Transaction Type beginning with "Decrease in Material Amount Due To..."
Use any relevant "M" code to remove the item from inventory.
 - Select the lot number you want by searching by the item description.

 - Complete the rest of the fields.
 - Repeat steps 1-6 for other items listed on the Purchase Order.
 - Open the Purchase Order that you want "removed".
 - Add an "Invoice" to cost the Purchase Order.
 - The Purchase Order can now be found under the "Costed Purchase Order" list.