Approvers can make some changes to PO such as rotate backup pages, change the order of backup pages and add back up pages to an PO before they approve the PO but they cannot delete pages.
Here is an article in our helpdesk on How to Rotate and Change the Order of Pages
Here is an article in our helpdesk on How to Add Backup Pages to PO
If any other changes need to be made to the PO backup images (like deleting) which the approver cannot perform, then the approver should reject the PO which will send it back to the original owner. The approver will need to add an appropriate comment advising why they have rejected the PO. This comment should indicate the changes that need to be made before the PO is resubmitted for approval again.