Q: Change Apple ID

You can click settings > icloud > sign out and then sign in with the correct Apple ID. Same with FaceTime, iMessage, iTunes Store, etc.

Or, if you mean that the iPod is asking for an Apple ID that you don't recognize, you can choose settings > general > reset > erase all content and settings. THIS WILL ERASE EVERYTHING ON THE IPOD.

Or, if you mean that you cannot get into the iPod because it's asking or an Apple ID that you don't recognize, you will need to contact the person you purchased the  iPod from to have them turn of the 'find my iPod' function.

If you are running into the Activation Lock

Find My iPhone Activation Lock - Apple Support

Then you will have to get the previous owner to do this

Turn off Find My iPhone Activation Lock - Apple Support

If yo can't then return for refund. Apple will only help if yo are the original purchaser