After you have chosen the teacher, there is no way of changing it back to the one you want. Sorry
Once your Tamagotchi is a teenager you can play Manhole. This game raises Spiritual points and it rewards you with 8 skill points if you successfully complete the game.
Yes, sadly once u have choosen your teacher thats that u can't change again. And well everyone else just said what else you need to know also there's certain foods that raise sprirtual points too. But be warned!! they also increase your tama's weight by i think 2LBS anyways here are the list of foods that raises spiritual points: