It’s easy, but first you must log into your account at www.google.com.
After you log in, simply click the link at the bottom left of the page that says Change background image.
A window will pop up that gives you a bunch of options that looks like this:
You can upload an image from your computer, grab one from your Picasa album (if you have one) or browse through the editor’s picks or public gallery to find your new Google background.
Now just click on an image, hit Select and marvel at the personalization power you have!
If you ever want to remove your Google background, just click Remove background image at the bottom left of the page.
~Andrew
