If you need to update your existing credit card information, or add a new credit card, you can do so from the Billing & Invoices screen. Click the down arrow next to your name in the upper right hand corner and select Billing & Invoices from the dropdown menu:
Choose the product you would like to update credit card info for, then click the right arrow to access the Billing & Invoices home screen:
Now click the Payment Methods button to bring up your credit card information:
From here, you can add a new credit card, remove an existing one, or edit your card info. (Please note that only the account owner will be able to update payment information, unless permissions have been granted to the user).