Click the image link relative to your desktop size.
Then right-click on the enlarged image and select "Set as Wallpaper".
Mac:
Click the image link relative to your desktop size.
Then click and drag the image to your desktop.
Next, from the Apple menu select "Control Panel", then select "Appearance".
Finally, select "Desktop," select "Add Picture," select the image you just dragged to your desktop, click "Set Desktop".
To determine the size of your desktop:
PC:
Right-click on the background of your current desktop, select "Properties," select "Settings" tab, see "Screen Resolution" for desktop size (e.g., 1280 by 1024 pixels).
Mac:
From the Apple menu select "Control Panel," select "Monitors," see "Resolution" for desktop size (e.g., 1280 x 1024, 85Hz).