I think that you can find several examples of characters who have changed throughout the drama. I would say that one of the best examples of this would be the Proctors. Certainly, the growth or change of Elizabeth and John would represent two characters who changed the most. Proctor's evolution lies at the heart of the drama. Miller constructs it so that Proctor's change is vital to the understanding of the play. When Proctor emerges at the start of Act I, one can only marvel at the level of change he makes at the end of Act IV. The very idea that Proctor can start off as "only human" and end the drama as something more than human is probably representative of the greatest amount of change. At the same time, I think that Elizabeth endures a great amount of change, as well. From one who is cold and angry at wrongs done to her by her husband, she emerges as one who understands the need for sacrifice and the need to make right that which is wrong. The fact that their marriage appears in very bad shape at the start of the Second Act and then becomes an unbreakable bond, even through death presumably, by the end of Act IV might represent yet another level of change in both.