A dynamic character is one who grows and changes over the course of a text (in this circumstance, a play). Based upon this, John Proctor is certainly a dynamic character.
Prior to the actual action of the play, John Proctor has committed adultery with Abigail Williams. Readers learn of this through a dialogue which takes place between both John and Abigail and John and Elizabeth. John's previous sin is deeply regarded by John; he feels remorse for his actions and has changed as a result of them.
John show his remorse for his action in the following quote:
God help me, I lusted.
Here, John is showing that he wishes to change based upon his asking God for forgiveness.
Another quote which speaks to John Proctor being a dynamic character comes from the scene where he is admitting to witchcraft.
I speak my own sins; I cannot judge another. I have no tongue for it.
Here, John recognizes the importance of the truth. John, again, admits to his own sins. He no longer wishes to hide them and turn from God. Instead, he knows ho important it is to be honest in the face of others and of God.
One last quote, which speaks to John Proctor being a dynamic character, is "No, no Abby. That's done with." Here, John is speaking to Abby about their affair being over. He knows what he had done is wrong and no longer wishes to commit such a sin. John's ability to push Abigail away shows how his will to stay true, from here on out, and how he has changed morally.