If you want  to change dates such as invoice date, due date, service description, add new service line or discount, timesheets, then simply edit the invoice and move it to DRAFT. An invoice in DRAFT allows editing these details, with the indication that you have to click on SAVE to see the changes. Subsequently, you can validate the invoice.

If the invoice is already validated and the necessary changes are substantial, it must be canceled and deleted so that it can be re-issued. But beware, the series already allocated for the bill in question is not unoccupied. To reset the counter so that the next invoice takes the same series, you must go to the configuration and change the next invoice number (see How do I set up the next invoice number).