PO Administrators and System Administrators can delete purchase orders. You must be the purchase order owner, and the purchase order must be in Purchase Requisition or Reset status to be deleted. 

Delete a Purchase Order

Open the purchase order, and assign yourself as the owner. Click Actions, and select Delete Purchase Order.

You will be prompted to confirm your action, select Yes to delete the purchase order. 

The purchase order can still be viewed in Deleted status using the Global Search function. You can revive a deleted Purchase Order by clicking Actions and Reset Purchase Order.