Web font data is updated when you republish your projects, therefore as long as you are a subscribing customer in good standing, you will have access to the most up-to-date data without having to purchase additional fonts or update your previous font selections or account settings.

Just access your project and republish it. If you are a legacy customer - fonts being delivered will update automatically. Customers self hosting will need to re-download the fonts and replace the instances of previously downloaded web fonts on their server(s).