Find your invoice
Select Edit in the Actions column of the invoice you wish to make changes to
Once the Invoice is open, find the line item you wish to edit and select Edit Amounts
If the Invoice has already been approved and issued you will be prompted that a Credit Note needs to be created.
Select Credit Invoice - The Invoice will be credited and a new Invoice created and opened
You may now edit the line item amounts and / or tax rates
Click Update to finish.