You can easily update your billing information on the website. If your card has expired, you should first remove your payment details, then update your billing information.

To update your billing information:

Log in on the website and navigate to the Dashboard

From the dashboard, click on Billing

In the Billing view, under Payment Method, update your card information and click Save Card

NOTE: If the Subscription was purchased from a Mobile Device or In-App, their billing information will instead be directly on the Mobile Device and will also have to be changed there as well.