Instructions
Press the "Xbox" button on the face of your Xbox 360 wireless controller. Your console's main menu will display on your television screen.
Select "Active Downloads" from the menu on the screen. This will show you a list of files that your console is downloading. This can include game demos, full games, movies, television shows or any other type of file you are downloading from the Xbox LIVE Marketplace.
Highlight your active download. Select "Pause" to pause the download, allowing you to resume at a later time. Select "Stop" to completely stop the download. You can now power off your Xbox 360.