Windows
Click the link of the image size to fit your computer's screen
resolution.
Right click on the image.
Choose the "Set as Wallpaper" option.
From the Start Menu, choose Settings and then Control Panel.
Double click on the "Display" icon.
Click on the "Background" tab.
Choose the "Center" option under "Wallpaper."
Macintosh
Click the link of the image size to fit your computer's screen
resolution.
Click on the image and wait until you get a pop-up menu.
Choose "Save This Image As."
Save the file to your hardrive (remember where you save it).
From the Apple Menu, select Control Panels, Desktop Pictures.
Click on "Picture."
Click on "Select Picture" and open the saved image.
Choose "Center on Screen" from the pull-down menu.
Click on the "Set Desktop" button