05-08-2013 08:11 PM
at the top of the screen, it says "My account". Click on that and then account settings. You'll have to sign in. Go to your "My account page". At the bottom of the page, it says "Payment", then default payment. Choose manage default payment. There you can change your credit card. Remember to save it.
These are the web from my pc instructions, the mobile version may be slightly different.