To edit a sale:
First locate the existing sale...
Go to "Sales" in the left hand menu and navigate to the appropriate day and click on the sale you want to edit.
Go to your booking calendar and click on the appointment to which the sale is attached. The click on "View receipt" at the bottom of the screen.
You will now be viewing the receipt for the sale. To edit the sale simply click on the down arrow at the top right of the receipt screen:
Then click on "Edit Sale" to start the editing process.
When you are done your edits click "Complete" to update the sale.