You can update the Payment method for your subscription with BURST by logging into your account on our website HERE.
While logged in you can select My Subscriptions, This will show you all the items you are subscribed to with BURST.
Here is a quick shortcut
Select the Address & Payment Details tab and then the Manage Payment methods
You can then add, edit, or remove a payment method from your account and assign your preferred payment method to your subscriptions.