replacing background image in Startup

Where is placed BIG background image? I am trying to replacxe that image but I don't can to find same! This image isn't placed in Media Libary and at this moment I don't can to find where to change that image with my... also I am interesting for precise size of background image.

Hi,

This image is located in the following directory:

wp-content/themes/Startup/images/header_bg.jpg

Please also remember to replace smaller versions:

http://demo.gavick.com/wordpress/startu ... tablet.jpg
http://demo.gavick.com/wordpress/startu ... mobile.jpg