Draft/Unpaid Invoices
Invoices that have been saved or are still unpaid can be edited easily:
Under the 'Invoices' tab, click on the invoice you wish to edit
Click the three dots at the top right and select: 'Edit'
Edit the invoice and save your changes
Paid Invoices
For invoices on which a payment has already been entered, you'll first need to remove the payment before you can follow the steps above to edit the invoice.
To remove the payment:
Under the 'Invoices' tab, click on the invoice you wish to edit
Scroll down to the history and delete the payment

The invoice will then be changed to 'Unpaid'
Follow the above steps to edit the invoice
You can then resend the invoice to your customer or enter payment