Can I edit or delete a note I added to an order?

You can delete a note, but you can't edit it.

1. Open the order from Orders → Manage Orders.
2. In the Notes box, find the note and click Delete on its right.
3. Type the corrected text in Add a note about this order… and click Add note.

The note is removed straight away, without a confirmation step, so check you've picked the right one. Comments posted in the Timeline can't be deleted.