If the status of the Purchase Order Approval Process is Active, then it is not possible to Edit/Delete since the buttons are disabled.
When a particular Purchase Order Approval Process is in Active status then it is not possible to Edit or Delete it. This is indeed system behavior.
If your requirement is to Edit/change the Approval Process, the you can follow the below steps:
1. Go to Business Configuration work center.
2. Select Overview
3. Search and open the Activity Purchase Order Approvals.
4. Highlight the approval process which you want to change and select Copy button.
5. In the new screen, update the changes that you intended to do.
6. Select Save and Close button. The status of this approval process should be Draft.
7. Now, select the old approval Process (Status = Active) and select Edit Validity button.
8. Delimit the old approval process and accordingly adjust the validity period of New approval process. Note: Make sure the date and time are provided correctly because the new approval process will become Active based on that Time.
9. Select Check button and Save the changes.
10. Based on the Time (which was provided by in above screen), the new process will become Active status and old approval process will become Ended status.
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