How to change your desktop background:

• Rightclick (Ctrl-click for Mac) on the image you want and choose 'Save link as'
• Save the picture in a place you can find back
• Windows:
• Rightclick on an empty part of your desktop
• Choose 'Personalize' (Windows 7) or the Desktop tab (XP)
• Windows 7: first click Desktop Background (lower left)
• Click Browse to go to your saved picture
• Choose the folder, click OK, then choose the picture
• Mac:
• Choose Apple menu > System Preferences and click Desktop & Screen Saver
• Click Desktop & Screen Saver
• Click Choose Folder to go to your saved picture and choose it