question about images

Hi, I’m new to WordPress and PHP so forgive me, but I am a designer who knows HTML. Just installed WordPress Uploaded new Theme, and I am trying to change background colors and/or background image. Looks like the page uses a BG tile called “kubrickbgcolor.jpg” but i cannot find it anywhere (my Dreamweaver crashes everytime I do a search through all files). The code on the style sheet says to check the index.php for images, but I cannot find any refernce there.

So, please help me — in simpleset terms possible — find out where the graphics are located and how you change and updated in the code.

Much appreciated, Jeff