To add multiple credit/debit cards to a profile, navigate to the profile's account page after signing in. On the left side of the browser, there will be an Account menu. Beneath this, click on Manage Payment Options. Here, you are given the ability to set which credit/debit card you would like your payments to default to, as well as the ability to remove and add other payment options. To remove a card, click on the trash can icon.
Users are also given the option of selecting a credit/debit card at checkout. After selecting "Pay with Credit or Debit" during a checkout, users will be given an opportunity to select from the cards that they have already added to their account, or they have the option of adding another card.