Parris and Hale flip-flop their positions throughout the play. At the beginning of the play, it is Parris who does not want to believe that witchcraft is occuring; he has just discovered Abby, Betty and other dancing and doing other questionable things in the forest. If that information gets out, it will put a black mark on his reputation, and people already don't like him in the town. He is desperate to keep that information hidden, and if Betty is declared "bewitched," he fears that the entire town will turn against him. He sent for Hale hoping Hale could debunk the rumors of witchcraft, so that Parris's reputation could be saved. Hale on the other hand, fully believes that he has discovered a cove of witchcraft. Tituba openly confesses, along with all of the other girls, and he is exultant that he was able to break the devil's hold on them, and to help them repent and turn away. He zealously goes about hunting down the supposed witches.
However, at the end of the play, Hale has done a complete turn-around. Proctor, with his pained confession of adultery, has convinced him of Abby's fraud and manipulation. He has seen the corruption of the courts, and realizes that all of the accusations of witchcraft were fake. He feels horrible; he feels that "there is blood upon my head," because he himself signed so many death warrants. So, he sets about trying to get the accused to confess in order to save their lives. Parris on the other hand, is at this time a believer in the witchcraft; throughout the play he has become an important figure of the courts, and feels pride and vanity over that role. For a while, people like him the better for it. He encourages and supports various accusations of witchcraft, doing all he can to aid and abet the courts in finding people guilty. So, Parris and Hale have, by the end of the play, done a complete role reversal when it comes to their opinions on the witchcraft.
I hope that those thoughts helped; good luck!