To edit an Invoice, you can go to Invoice Editor either by clicking 'Edit Invoice' in action button sections on Invoices page or by clicking 'Edit' button on View Invoice page. This should take you to the Invoice Editor page.
Once you are in Invoice Editor, you can edit any details you like and can also add or remove line items. When you are done with the Editing, you can save Invoice and resend it to the customer.
That's all about the Invoicing section. Feel free to write us in case of any issues or queries.