How did Macbeth and Lady Macbeth change over the course of the play?
They change a LOT. Answer below.
I think it's arguable to say that Macbeth and Lady Macbeth really switch personalities throughout the play. I say this because Mac, in the beginning, is unsure, hesitant, and even timid when he stares the concept of committing the murder of a King in the face (which is a fair reaction, obviously, but maybe a little silly coming from the man who is very skilled on the battlefield and used to mass murder but y'know). An example of this is here:
"Upon the sightless couriers of the air,
Shall blow the horrid deed in every eye,
That tears shall drown the wind. I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o'erleaps itself
And falls on the other."
Here, Macbeth admits to feeling unmotivated to jump and kill Duncan. He has a wary conscience, which alone says a lot about his character in the beginning. He knows what he's doing. He's conscious of it all.
And then you have Lady Macbeth, who is actually horrifying. Like, she is scary. She is very ambitious. There isn't a lot for women to do in Scottish society other than the typical old-age of being a mother at home and a supportive wife. But there is stuff for QUEENS to do. I imagine the fact that her husband might become King being very exciting for her. Here are some examples of her character from the beginning:
"I have given s.uck, and know
How tender 'tis to love the babe that milks me:
I would, while it was smiling in my face,
Have pluck'd my nipple from his boneless gums,
And dash'd the brains out, had I so sworn as you."
Lady Mac is explaining her that she would not not do something if she swore to do it. She is very intense and very much unlike her husband. That brief (and, again, horrifying) blip from one of her monologues along with her "unsex me here" speech from earlier in the act really says a lot about the intensity of her character.
However, the events of the play really do change them. I said before that their personalities swap because Macbeth becomes a bit bloodthirsty and almost as intense as his wife was in act 1. All of these repeated murders made him into a desperate, paranoid, anger man. An example:
"I will not yield,
To kiss the ground before young Malcolm's feet,
And to be baited with the rabble's curse.
Though Birnam wood be come to Dunsinane,
And thou opposed, being of no woman born,
Yet I will try the last. Before my body
I throw my warlike shield. Lay on, Macduff,
And damn'd be him that first cries, 'Hold, enough!'"
Macbeth, who in my previous answer was literally saying, "I don't know about this." has taken his wife's advice seriously to heart by saying, "I started this, and although all odds are against me right now, there is no way in hell I'm giving up, even though my life is on the line." It is a bit of a bittersweet thing, because he finally throws out his consciousness. He doesn't know where to draw the line so he takes it too far.
Lady Macbeth, as I mentioned, takes on her husband's personality as well. A woman once intense begins to feel the guilt of her actions and her manipulative ways, and we see this in a scene where she technically isn't conscious.
DOCTOR: What is it she does now? Look, how she rubs her hands.
GENTLEWOMAN: It is an accustomed action with her, to seem thus
washing her hands: I have known her continue in
this a quarter of an hour.
LADY MACBETH: Yet here's a spot. ...
... Out, damned spot! out, I say!--One: two: why,
then, 'tis time to do't.--Hell is murky!--Fie, my
lord, fie! a soldier, and afeard? What need we
fear who knows it, when none can call our power to
account?--Yet who would have thought the old man
to have had so much blood in him. ...
... The thane of Fife had a wife: where is she now?--
What, will these hands ne'er be clean?--No more o'
that, my lord, no more o' that: you mar all with
In her sleep, Lady Macbeth is haunted by the nightmares of her guilt. Even her gentlewoman has noticed that Lady Macbeth washes her hands obsessively in order to try to remove the (metaphorical) bloodstains that her and her husband's actions have left. She is uncertain, frightened, and timid like Macbeth was at the beginning of the play.
I hope this helped you. Lemme know if you need anything else!