To change the background, you must first upload a background image to your photo album. Here's a brief how to:

  1. Go to Add Album
  2. Select Profile - Pictures used to modify your profile style and click "Submit"
  3. Following instructions to upload your background image
  4. Find out the location (URL/address) of the uploaded image
  5. Go to Customize Profile
  6. Enter the URL/address of your background image (under "main" heading) and click "save"
  7. Your profile should now display your new background

If you have any further questions, please don't hesitate to ask.