Setting Primary/Backup payment method
You can change the primary method as well as add/set a backup payment method if your primary payment method fails.
The credit card/PayPal account you add when you sign up with a premium plan is set as the primary payment method. To change a primary method, you'll need to add another Card/PayPal account and set it as the primary payment source.
A backup payment is added the same as above, however, you'll need to select the Backup option instead of Primary and update. You will then have two payment methods, a Primary and a Backup to keep your subscription active and uninterrupted.