If you need to change things like billing email, a new credit card number, etc. you can do it by going to Configuration > Account Settings.
Both billing notification email address and the billing information can be changed there.
If you need to do this, but can’t access the Account Settings screen, then you’re not logged in as the account owner. Only the account owner can make changes to the billing information, so you need to either log out and log back in with the account owner credentials OR find the person who has the credentials to make the change for you.