If your on an iPhone, open the iPhone sized image. Press down on the full size image till a dialogue box appears. Then press the button “Save Image.”
Any additional questions on how to make or download wallpapers to you’re iPhone, please refer to Apple’s iPhone How To section at Apple.com.
If you are on a Droid, open the Droid sized image. Save the image to your phone. Open up the image in the gallery application. Find your desired image. Click on "Set as" > "Wallpaper". Then press and hold your finger on the orange 1px border that is around your image and drag that line to the top of your screen so you get 100% of the image. Press "Save".