Within an event's guest list, you can tap anywhere on the guest's name to open their profile card.
Once you're on the guest's profile card, you'll be able to quickly view information, such as the guest's attending status, VIP status, email address, +1s, Lists, and Notes.
It's from this screen, that you can star/un-star the guest as a VIP, add a +1, or add notes.
By tapping the top of the Ticket stub at the bottom, you'll be able to view all details submitted during the RSVP or ticket buying process.
You can see that for a ticketed event, the More Info screen contains Order Details, although that information is not editable — only the Guest Info is.
Tapping the EDIT button will allow you to edit previously submitted RSVP or ticket registration information.
All of the information on the below screen is editable; just hit the SAVE button on the RSVP form to save your changes.
Update: As of 4/19/2017, you're now able to change a guest's status (i.e. Attending to Not Attending) directly from the app. Check it out!