Right click on whichever smiley image on the left you want to use.
Click "Set as wallpaper" or "Set as background."
If you're using a Mac:
Move your cursor over whichever image on the left you want to use, hold your mouse button down until you see a menu and select "Save This Image As."
Then choose where you'd like to save the image.
Go inside your apple menu to control panel, and select "appearance".
In appearance, select Desktop, than click "Place picture."
Select the image file you saved and click "Choose." Select "Position Automatically."
Click "Set desktop" and close the window.
If you're using Linux/Unix:
You're smart enough to know how to do this without any instructions.
I'm Evil Smiley, and this is my blog -- where I plot to destroy the world, research my targets and generally just brag of my incredible accomplishments.