If you've created an invoice in error and wish to delete it, you will simply need to select the invoice on the left of the patient account history and choose the trash can in the top left corner.
You will be prompted to confirm that you wish to delete the invoice and then to give a reason for the deletion.
Please note: You cannot delete an invoice with any payments or credits on it. You would first need to remove the payments/credits before deleting the invoice.
Before deleting any invoices, we would recommend you read our Deleting Payments and Invoices article