To add a new card or to delete your linked cards, go into the menu in the upper left corner of the screen, and find the 'Registered Cards' section. Click on 'Edit' in the upper right corner and from here you will be able to delete your linked cards. Click on 'Add a new card' at the bottom of the screen to add your card. You can either scan your card for quick linking or you can manually type in your card number.