Instructions
Sign in to your Xbox Live account on the Xbox 360 if not already signed in. An Xbox Live account and an Internet connection are necessary to download a demo. Verify that your flash drive is also plugged in to the system at this time.
Navigate to the Games tab on the Xbox 360's main menu.
Select "Browse Games" and select the "Demo" tab.
Select the demo you want to download to your flash drive. Click "Download" and then "Confirm Download."
Select your flash drive as the location of your download in the Storage Devices window. The game will begin downloading to your flash drive immediately.
Launch your game demo by selecting "My Games" from the Games tab and choosing the demo you want to play once the download is complete.