Currently, no changes can be made within the Yapp app, except to dynamic pages like News Feed, Poll, and Crowd Pics. As the admin, you can delete or broadcast posts on the News Feed, and you and your users can all post into that page as well.
Once you publish, the app will automatically update on your and your guests mobile phones. If you've got Yapp open, you may need to drag down to refresh your Yapps. Then, any changes to your app (e.g. new pages, schedule changes, theme changes, etc.) will be updated.