To set an image above as your wallpaper, click on the link below the wallpaper image that you would like that matches your monitor's screen resolution. In the window follow the instructions below for your specific operating system.
Windows - Right-click on the image and select "Set as Wallpaper"
Macintosh - Press the mouse button on the image and hold the mouse still until a pop-up menu appears. Select "Download Image to Disk" or "Save Image as ..." Once the image is saved, go to Appearance control panel and use the Remove Picture and Place Picture options to select it as the Desktop Picture.