Note: This action can only be taken by Account Owners or users with "Can view and manage billing settings" permission enabled. Read this article to learn how to give proper permission to other users so they can change billing settings for the account if needed.
Billing info can be changed at the Usage and Billing page, you can find this page under Account Setting Section on the left navigation.
Inside the Account Details page, click on the change link under Billing Information section:
After that, you will see a popup modal allowing you to re-enter your billing information.
All the new information you enter here will overwrite the existing billing information in your account. The Account Details page will be refreshed upon successful update of your account's Billing Information and you should see them displayed on the page.