To update the billing details for your Intruder subscription, just go to the Billing page, accessible from the bottom left of the portal:
Under Billing details, you can update your payment method:
Clicking on Update 'Billing Details', will allow you to amend the email address; company name; address and VAT ID.
Any updates will be reflected on your next invoice.
(It's not possible to amend invoices that have already been issued).