You may change the PayPal account or credit card associated with your product by going to the Usage Intelligence Dashboard > Administration and under Quota, Billing and Invoicing select Set Payment Method.
Note for PayPal users: If you would like to change the bank account or credit card details from which funds are withdrawn by PayPal, you must do this by logging into your PayPal account and using PayPal's control panel.
PayPal Credit Card validation: Once you define a new payment source on your PayPal account, you must first verify your card/account before you can make your first payment. For more details please visit this KBase article: Verifying your PayPal payment source.
All premium accounts must have a valid payment method defined. This is required by the billing service at the end of your billing cycle.