A posted invoice can't be edited. To correct one, issue a credit note or reverse it, so the original and the correction both stay in your records.

Situation	What to use
Part of the invoice was wrong, or goods came back	A credit note for that part
The whole invoice shouldn't exist	Reverse the invoice
The customer overpaid and wants the money back	A refund from their credit balance

Issue a credit note

Open the invoice and choose Actions, then Credit note.
Choose the lines and quantities you're crediting.
Save and post. The credit reduces what the customer owes, or adds to their credit balance.

Refunds

A refund pays a customer's credit balance back to them and posts to the correct accounts automatically.