The ability to edit the delivery note in QuickBooks Online (QBO) is currently unavailable. I can see how having this option would be helpful for you and your business. Rest assured I'll pass along your suggestion to our Product Developers. They're always looking for ideas to consider on how to improve QBO.
In the meantime, I recommend visiting our Blog site. This is where we share recent happenings and future developments, such as updates to newly added features.