Hi
Do you mean after receiving them. Like you ordered 200 and received 198?
1) Then you need to change the QTY to 198. If you have the Delete Purchase Order report in job queue this will delete the PO
2) I heard some companies manually delete these PO
One note is: you may need to archive the order first for future use .
If you receive the full QTY than that line consider close for BC. But PO may still open if it has other lines open in it. If no other lines then you can use Delete Purchase Order report (or set it in Job Queue) to close and delete the PO.