Step 1: Click the Account Settings icon on the menu to the left.
Step 2: Scroll to Payment Methods, then click the blue Edit button.
Step 3: On the next page, make the necessary changes to your billing details, then click Update Billing Address. If you only need to update your credit card details, skip this part and scroll down.
Step 4: To update your credit card details, enter your new credit card number, expiration date, and CVC. Review what you've entered, and click Update Credit Card.