Hi Fabia,
This depends a bit on the state of your invoice. If you've only confirmed the invoice but haven't registered payments and haven't sent out the invoice your best bet is to probably cancel the invoice. Click on the "Cancel" button at the top of the invoice to do this. It may require you to change your journal so it allows canceling entries. You can do this from Accounting > Settings > Journals by checking on the option "Allow cancelling entries": https://imgur.com/Kwl1Yk1
Once the invoice has been cancelled you can click on "Reset to draft" and you can then modify your invoice with whatever changes you'd like.
If you have already sent out the invoice or have registered a payment you should use the "Add credit note" button to credit the invoice and then create a new invoice with the right values.
Regards,
Yenthe
How to change a customer for a posted invoice in Odoo 14?