How to Add/Change Payment Method

To change your credit or debit card, you can log in and then go to Payment Methods on the left hand side of the page.  There you can add a new credit card to be selected at checkout.  You can also delete payment methods from the account in that spot.  

During checkout, you also have the option to change the payment method during the Billing step.  Where you see your card, you'll also see a blue link to change that payment method.