How to change my Primary Credit Card for my account
To change your Primary Credit Card, be sure to add a new Credit Card to your account. Once you have done that, you can select the circle next to the secondary credit card. By doing that, it will automatically save to be your new Primary card for your account, and will be the one charged should you be autocharged for items that you have won.
Note: On the app, you can not change the primary credit card. You must do this on the browser.