You can't back up your game to reinstall it on another computer. All you need to do is to start playing a new game on your new device. If you are connected through facebook or twitter then your city should load once you have completed the tutorial. From there you will need to contact GI so they can register your game to restore your port, VIP, corp and social functions. If you are not connected through facebook or twitter then you will need to contact GI and give them your support id's from the old and new games. The only kind of transfer that is not possible is between different platforms, so no windows to Android. Hope this helps. If you're on Android and have difficulty with the transfer come and find me as I am a moderator, look for cocos paradise.