Help with macbeth Monologue!!?

We need to write a monologue about a character in the play macbeth. My chosen character is macbeth i need to choose a monologue that is more that 2 minutes and i need to show how the character changes in the monologue and i also have to act it out. im thinking of doing the part where macbeth writes the letter to lady macbeth ( they met me in the day success...) but im not sure how to show the change in character.