You can change your payment method by logging into your account, going to Billing, and clicking on “Manage Billing”.
Once you click the button, you’ll be taken to a separate page containing information about your subscriptions and payment methods.
If you are a Stripe user, click on “Add payment method”:
Enter your debit/credit card information:
To change your default payment method, select “Use as default payment method”.
If you are a FastSpring user, click on Manage >> Update payment method:
Then, add your new payment method: