To set one of the images as your wallpaper, simply click on the correct resolution size. When the picture appears, right click with your mouse, and select "Set as Desktop Background".
Wallpaper for the iPad, iPhone, and other mobile devices
To set wallpaper for your iPad/iPhone, tap on image. Once the picture loads, tap image until the Save Image/Copy option appears. Save the image. Go back to your Photos app and bring image up. Tap on the little white arrow popping out of a box (next to the slideshow and trash options) and choose Use as Wallpaper.