To change the background image or color behind your site:
In the Theme Prefs section of the XSites Wizard, click the Change Your Background link.
From the options provided, choose to use one of the Provided Background images, Solid Colors, or to Upload Your Own background image.
Select one of the provided backgrounds, a color, or click Select an Image and browse out to the background you want to use on your site.
When finished, click Save and Close to update your Theme Prefs.