PC using Windows: Once the image you selected appears on the new window that opens, right-click on the image and select "Set as wallpaper" or "Set as background".
Macintosh: Once the image you selected appears on the new window that opens, press "Control" and click on the image. Then select "Download image to disk". Save the image in the location you want. Go to "Apple menu", choose "Settings" and then "Display". At the "Office" tab, click on "Add image" and search for the file you downloaded earlier. Press "Set Office" to finish the wallpaper change procedure.