Just log into your account and in the top menu, go to My OA > Dashboard > Account.
Or, follow this link: http://oatleyacademy.com/account/
Scroll down and you will see your orders, and under that a Renew or Change Payment Method button. Go ahead and click that, and in the next screen you can enter your new card information.
After checking out, a charge for the next month will be issued and your renewal date will be moved. And don’t worry, you won’t be charged double for the month.