Making all sections in a web page one picture

Hello, I am using the expanded theme “band” and am trying to edit my about page. I really like the way they have it- where the entire page has a backround of one photo. However, I can’t figure out how to change the picture they have (some guy crowdsurfing) and make it my own photo. Help please??
URL :http://borntobewandering.com/x/#/content/224

Hi,

You can add it under Page Settings.

OR you can also add it Under Cornerstone > Settings

Hope that helps