Right click on the size required under the image you want to download and 'save as' to save to your pc (ctrl + click on a Mac). Then go to Control panel > display > desktops and select the image (Sysytem Preferences on a Mac)
800 x 600 pixels
1024 x 768 pixels
1280 x 1024 pixels
1600 x 1000 pixels
1900 x 1200 pixels
800 x 600 pixels
1024 x 768 pixels
1280 x 1024 pixels
1600 x 1000 pixels
1900 x 1200 pixels
