You can manage your billing from the Dashboard by clicking on 'Settings'-->'Add-Ons and Billing'-->'Billing Management':
(Note: Prices displayed are for demonstration purposes.)
- Click the "+Add Credit Card" button to add a new Credit Card.
- Click on the existing payment method if you want to remove a payment method. Note that you must have at least one payment method.
- Click 'Save' when you have finished managing your credit card.
- Click 'Done' when you are finished.