If you signed up via the website, you can manage your subscription through our interface. If you're being invoiced, you'll want to contact your Account Manager directly. If you're not sure who that is, our Customer Success team can assist you.
To update your billing information, click on "Account" in the upper right hand corner, then "Update your payment information".
The next page will allow you to change your credit card, update the billing contact, and update the billing address associated with your account.