How do customers update the shipping address?

On the main subscription management page, there is an option near the top for Addresses. 

After you click Addresses, you will see all the shipping addresses associated with your subscription. You can click the pencil icon to Edit an existing address or click the Create New Address button to add a new one. 

A drawer will appear on the right side of the screen for you to add or update any address information. A phone number is required for all shipping addresses. Click Submit once you've added all required address information.