To change order details, click "Edit" at the top. You can change buyer information, delivery method, remove or add a flag, mark as fulfilled/unfulfilled, and change any custom information provided by the person who placed the order. To change attendee details, click on the "Edit/pencil" button beside the attendee's name and all fields captured for that attendee will be available to amend.
Don't forget! Click "Save" at the top of the page when you are finished or your changes will not be saved to the order details.