Depends on whether you're using Windows or mac. You've gotta be specific with questions like this... If you're in windows, save it somewhere, right click, and click "set as wallpaper." For other wallpaper settings, right-click on the desktop and click "properties." If Mac, then save it somewhere, open system preferences, click the "Desktop/Screensaver" pane, then "choose folder." Choose the folder it's in.
