Which characters change in the play Twelve Angry Men, and what causes them to change?
Your term, "change", has some interesting inferences. If you mean change, as in which jurors changed their final vote--three jurors changed their minds. The final vote was 9 to 3 for acquittal. You can find the exact vote in the link I've provided.
The more in depth part of the question is which jurors were most changed because they participated in the trial. This requires deeper reading. Keep your characters' original opinions clear in your mind. I would suggest a T-chart where you can list the characters down one side and the ways they changed on the other. I would also keep track of the Acts where each character changed.
The link below should help you sort out both parts of your teacher's clever question.