How i can change background of my website?

Hello,
How i can change background of my website?Because i have not much knowledge about this and i purchased this website from a company but now i want to change its background.

 

There is a file called style.css on your web folder, Open it and you will see this code :

Code:

body {
background:url("images/[COLOR="Red"]background.jpg[/COLOR]") repeat scroll 0 0 #000000;
font-family:Arial,Helvetica,sans-serif;
font-size:12px;
line-height:16px;
}

change the Red colored to mach your new background image