There are two ways to delete an invoice:
On the Manages Invoices list view
Select the invoices you wish to delete using the checkbox on the left hand side. Once one or more invoices have been selected, you will see the option to delete invoices at the bottom of the table.
On the individual edit screen
You can also delete them by going into the individual edit invoice or edit quote screen and selecting ‘Delete Permanently’. This will delete the invoice or quote.