No worries-- just go to the "Account" section and then to “Edit Payment Methods”. If you’ve paid with a credit card, your card will appear as the subscription card. Click on the "UPDATE SUBSCRIPTION CARD" button next to your subscription card to edit the info. Then update your info and save it. All of your future payments will be processed with your updated card.
Keep in mind that adding a new saved card on this page is for future à la carte purchases. This doesn't affect your subscription card.
If you paid using PayPal, just update your information from your PayPal account. Once you do this, all future payments will be billed directly to your PayPal account.