Instructions
Select the "Settings" tab of your Xbox 360 dashboard and select "Account."
Select "License Transfer" in the Your Billing Options menu.
Press "A" to begin the license transfer. Once complete, press "A" again to view your download history. You will need to download previously purchased software again to update the licenses.
Select the item you want to download and select "Download Again." Download all previously purchased items to complete the license transfer process.