Click on the gear icon at the top right corner, scroll down until you see "Orders" and tap "Order forms". Here you get an overview of all your order forms.
Change a form
Find the line with the order form you want to change, click on the pen, make the changes and click on "Update".
Archive a form
Find the line with the order form you wish to archive and click on "Archive".
Restore a form
Click on "Show archived", find the line with the order form you wish to restore and click on "Restore".