WINDOW USERS:
Select the file 640 x 480, 800 x 600, and / or 1024 x 768 after open, right click and select (set as wallpaper), and there you go.

MAC USERS:
Select the file 640 x 480, 800 x 600, and / or 1024 x 768 after open,drag the file to your desktop. Open up you appearance. Go to desktop tab. Then select place picture. Then go to your desktop and select the file. If using OSX, open System preferences. Click on Desktop & Screen Saver. Click on Desktop. On left side of window click on Choose File. Navigate to where you saved the wallpaper and choose it.