Instructions
Transferring via the Internet
Turn on the Xbox 360 to which you want to transfer your gamertag.
Press the ̶0;Guide̶1; button on your Xbox 360 gamepad to open the ̶0;Home̶1; menu.
Use the d-pad or left analog stick to scroll down to the "Recover Gamertag" option and press the ̶0;A̶1; button.
Press the ̶0;A̶1; button again on the ̶0;Recover Gamertag̶1; screen to confirm the transfer of your gamertag to another console.
Highlight ̶0;Yes̶1; and press the ̶0;A̶1; button when asked if you want to exit your current session. This will log you out of any active profiles that are currently active.
Press the ̶0;A̶1; button to continue, and use the onscreen keypad to enter the e-mail address (your Windows Live ID) that you used when you created the gamertag. Enter the password and then select ̶0;Done.̶1; Your gamertag will be retrieved to the Xbox, along with all the achievements you have unlocked.
Transferring via a USB drive
Switch on the Xbox 360 game console that holds the gamertag you want to transfer.
Connect the USB drive that you are going to use to transfer the gamertag to an open USB port on the Xbox 360 game console.
Use the d-pad or left analog stick on your gamepad to scroll through the options on the dashboard until you reach "My Xbox." Scroll to the right until you reach "System Settings," and press the "A" button.
Scroll down to "Memory," and press the "A" button and then highlight "All devices." Then press "A" again.
Scroll down to "Gamer profiles," and press the "A" button. Highlight the gamertag you want to transfer and press "A" again. Select "Move" from the menu that appears.
Repeat the process for moving the gamertag as you did previously, but this time select the hard drive of the new Xbox 360. If you leave the gamertag on the USB drive, the USB must remain connected to the Xbox 360 to use it, so it is better to move it to the hard drive.