The account owner is the only user who has access to the billing settings.
The billing section is found under Settings > Organization > Billing.
The billing summary lists all of the active users that you are being billed for and at the top of the page, you can choose between the monthly and annual billing options. You can enter your card details in the lower left corner.
Account Management - Change Owner
Under manage account the current owner can transfer the account ownership to one of the other active users.
Account Management - Invoices
All of the account invoices can be viewed and downloaded/printed from the invoices section.