Microsoft recommends that Xbox 360 users update their consoles with any new firmware release. If you have updated your console and no longer wish to use the updated version, you can restore the console back to its factory defaults. Restoring the Xbox 360's factory firmware is not recommended by Microsoft and can void any warranty. There are a number of actions required to trigger the console into factory default mode.
Remove any memory cards and USB drives from the Xbox 360. Power on the Xbox 360.
Go to the Xbox 360 main menu. Click "My Xbox."
Scroll over to "System Settings." Then select "Console Settings."
Scroll down and select "System Info" in the Console Settings menu.
Press the following key combination: "Left Trigger," "Right Trigger," "X," "Y," "Left Bumper," "Right Bumper," "Up," "Left Bumper," "Left Bumper" and "X."
Select "Yes, reset settings" on the Reset System Settings page. The console will then restore itself to its default factory firmware. Once restoration is complete, the Xbox will prompt you to select your language and other user options again.