you've either got to create a new image and replace the one above or, remove reference to it in the css. by doing so, you'll lose that background image and be left with the main background of the template
Not sure if it will validate like that as the css file references it also, but you should be able to comment that out in the css as well. Got rid of that extra bit of whitespace that was left when I did it though..... ;D
Do not go where the path may lead, go instead where there is no path and leave a trail.