To update the credit card information associated with your account:
 
Log into your account
Click the "Account" tab
Choose the "Credit Cards" subheading
Choose to "Add a Credit Card" and enter your credit card information
Click "Save Credit Card"
 
After you have successfully added your credit card, you have to modify you current subscription:
 
Click the "Account" tab
Choose the "Subscriptions" subheading
Click "Actions" on your active subscription
Choose  the “Change Billing Information” Option
Choose the new credit card you just added to your account.
Click "Submit Changes"