change backgrounds

I`m using the free version of musicmachon theme an would like to know how to change the background image.
The default background image consists of 3 parts. 1)crowd in a redish light 2)guitarplayer in a bluish light and 3)guitarplayer in a smokey greyish light.

How can I change this background and insert my own 3 images ?

Thank you for your help in advance !