How to properly close a Purchase Order?

 Good day. We are looking to close various approved purchase orders and are wondering what is the proper way to do so? Can anyone advise on how to properly close out purchase orders in the following senarios? We will not be invoiced any further for these PO's but we want to make sure that we keep a record of the initial purchase order so we don't want it deleted out of the system. Thank you.

-Purchase orders with no receipts or invoices. Can this just be closed or cancelled?

-Purchase orders with receipts but no invoices billed against it. Does the receipt need to be reversed first or can it just be closed or cancelled?