If you need to edit the billing information on your account, first ensure that you have permission to access the billing information. Only admins and owners have permission to view billing, and only owners have the ability to edit billing. Read more on user permissions.
Once you have logged in you will go to the billing tab within your organization dashboard. On the right column you will see an overview of the current billing information and an edit icon in the top right.
The modal will allow you to view your payment methods and select between them if you have multiple. Or you can add a new payment method.
Then you will be able to add and save a new payment method.
For Shopify Customers
If you are utilizing Compose via the Shopify application, you will manage your payment method within the Shopify Admin panel, not within the Compose dashboard.