Step 1: Click on the link to select the image size you want to download.
Step 2: "Right click" on image and choose either "Set as Background" (in Internet Explorer) or "Set as Desktop Background" (in Firefox).

PC Instructions (Chrome)

Step 1: Click on the link to select the image size you want to download.
Step 2: "Right click" on image and select "Save image as."
Step 3: Navigate to your desktop pictures folder and save image.
Step 4: Click the Start button, then Control Panel, then Personalization, and then Desktop Background.
Step 5: Click the picture you saved to select it as your desktop background.
Step 6: Click "Save Changes".

Mac Instructions

Step 1: Click on the link to select the image size you want to download.
Step 2: Right click (or control-click) on image and select "Use Image as Desktop Picture," (in Safari) or "Set As Desktop Background" (in Firefox).