Full Instructions
On How To Change Desktop Wallpaper

First: At main page select wallpaper and click the button under the picture wanted.
Second: A new window will appear with the actual image to download.
Third: Right click on image and select Save Picture As. (Save image to Desktop.)
Now that you have downloaded the image you must set as desktop background.
Fourth: Right click on your desktop and a menu will appear.

Fifth: Select Properties.
The Display Properties window will appear.

Sixth: Select the tab Desktop.
Seventh: Click on Browse button and find image downloaded on Desktop.
Eighth: Click on Apply and just wait until desktop becomes image downloaded.