Invoices generated through Coworks have many different states discussed here.
Currently there is no way to edit an invoice once it has been sent. You can delete an invoice before it sent to the customer while in the "scheduled" state.
Once an invoice has been finalized, your only option is to close the invoice by selecting "close" from the invoice actions dropdown and then create a new one.
If the invoice has already been paid, you can issue a refund for the invoice and create a new invoice for the desired amounts