QUESTION Theme: GreyOnePage : Background-pics

[medienkerl]

Hello! 

I will use GetSimple CMS for an OnePager. So I try the Theme: GreyOnePage. http://get-simple.info/extend/theme/grey-onepage/793/ 

Actually I installed this Theme. 
It is working with text. This is ok. 

My question is: How can I put pictures in this theme? 

Is there a short introduction, how I install the background-picture and some more pics? 

Thanx for your help. 

Greetz, Rick
(medienkerl) 
Ich spreche deutsch - I speak english.