Add a background alltuts theme

hi,
I would like to change the background of my blog, the theme i’m using is Alltuts (this http://wordpress.site5.net/alltuts/).
The code is this

BODY STYLES
———————————-*/

* {
margin: 0;
padding: 0;
}

body {
color: #333;
background:#f0f0f0 url(images/bk_body.png) repeat-x;
font-family:Arial, Helvetica, sans-serif;
font-size:13px;
line-height:135%;
}

This is a sreenshoot http://img855.imageshack.us/img855/4360/backgroundic.jpg
#f0f0f0 is the html color of backround that I’d change with an image,
bk_body.png is the backround header. (this http://img843.imageshack.us/img843/5267/bkbody.png)

How can I can change the color of background with an image?
Thank you