To edit quantities on a PO, click on the edit icon next to the PO you want to change from the Purchasing page.
Make changes to the quantities (step 1) and click on Update (step 2).
NOTE: You can only modify a Partial PO down to the quantity received against it. Once the quantity received equals the quantity on the PO, the PO will be closed.
To delete a Draft PO, click on the Edit icon next to the PO you want to change from the Purchasing page. Click on the trash can icon and confirm you want to delete the PO.
To delete an Open PO, click on the Edit icon next to the PO you want to change from the Purchasing page. Click on the three vertical dots at the top. You can either mark the PO as completed, or you can delete the PO.