To find your Apple ID and password, you can use the password retrieval process at My Apple ID. Click "Manage your account" and then click "Forgot your Apple ID?" on the sign in page. After that, complete all the required fields and then choose one of the options presented.
Uptade your iPod to the latest version, Then when you sign in your apple I.D in settings there should be a bar at the bottom that says iforgot ,tap on it and it will tell you everything you need to know on how to change it... Hope it helped