You can update your billing information with your account. Once you've logged in, click on Account > Billing to review your billing information. To edit your current payment information, click on the pencil icon to the right of your credit card's last 4 digits.

You can add one additional form of payment, should you need to switch payment between two different credit cards. To add an additional credit card, click on the "+ Add Payment Method" button below your credit card information.