Note: This action can only be taken by Account Owners or users with the "Can view and manage billing settings" permission enabled. Read more about account permissions and how to update a user's settings.
Billing information can be changed in Usage and Billing, which can be found under Account Settings in the left navigation.
On this page, click on the change link under Billing Information:
A modal will be shown where you can update your billing information.
After entering in your new billing information, all existing billing data in the account will be overwritten. The new billing information should now be visible when the modal closes.