The Dynamic Background module "enables site administrators to upload a range of images and select one as background on the site. This enables non HTML/CSS aware administrators to quickly change the background image on a site from within the administrator interface".

Below you see some screenshot´s of the Dynamic Background-Module.
Click on the images to open a new window with full size preview.

Step One

Install the module in the normal Drupal way. After you have installed the module enable it on your site.

Step Two