Summary: 

Editing the "Purchaseorderlinesgrid" field via the document designer. 

Steps:

1. Double click Purchaselinesgrid
2. This will shift to the Component tab
3. Check under Column Control
4. Scroll in Headers menu
5. Highlight headers you want to remove/add 
6. Untick/Tick Visible box
7. Click Save
8. Click Publish

Additional Information:

Further edits can be made on the header ordering, header name, width, etc. 

Changes to the layout will be reflected for everyone and on the printed  and emailed copies.