Background Image

I have downloaded (applied) a template from themify called iTheme2. It was free and it looks nice. See eadscolorado.org

However, we want to change the background image. In the Dashboard, there is a styling setting for this theme in it’s settings, but it puts the jpeg image at the top center of the page as a thumbnail or else stretches image out over entire background of webpage that it looks too cloudy/grainy. Does anybody know how to successfully change the background image from this theme? I can’t even get it to change to a solid color. I can’t go to the support forms on themify because I haven’t purchased a theme. This one was free. Thanks in advance if you can help!