1. Right click the desired screensize link and wait for the download options
2. Select 'Save Target As' and take note of the location you are saving to.
3. Remeber the file location you saved it to, if the .zip has not uncompressed itself, double click the .zip file to uncompress the JPG image.
4. Go to your control panels or system preferences to select the JPG image as your desktop.

Mac users:

1. Click and hold the desired screensize link. [or 'Right Click', or 'Control Click']
2. Wait for the link options menu to appear.
3. Select 'Download Link To Disk' taking note of the location you are saving to.
4. Remeber the file location you saved it to, if the .zip has not uncompressed itself, double click the .zip file to uncompress the JPG image.
5. Go to your control panels or system preferences to select the JPG image as your desktop.