During act 1, what are the things and how do they cause Macbeth to start having thoughts of killing the king to get the throne?How does this change him from innocent to a murderer.
How far can we say that Macbeth was innocent at the beginning of the play? He was a "war hero" as shown in the extremely cruel scene in the early pages of the play. He took the place of a traitor, the thane of Cawdor. It may not have been mere coincidence if he did... and eventually betrayed the King, Duncan. As a matter-of-fact, he was merely playing a part, that of the hospitable host.
Next, when the witches appeared and uttered, not a threat, but a prediction that sounded very much like one - since he was chosen as king but Banquo's children, not his, would reign after him - he was most certainly tempted and yielded to temptation. The witches and Lady Macbeth, who has often been considered "the fourth witch", be/witched him. She became wicked like the witches who are also called "the wicked sisters" in the play. They are a reference to the Fates.
Finally, King Duncan's death is probably linked to the symbolical death of the father figure as it is explained in Freudian terms. The sexual attraction that never ceased to exist between Macbeth and Lady Macbeth is, indeed, another factor that accounts for this lust for power.
It is nevertheless true that Macbeth felt remorseful after the murder and even wished he had not done "the horrid deed". It was Lady Macbeth, at this stage, that was ruthless and considered Macbeth's "horrible imaginings", ghastly visions or "false representations" (like the dagger) as projections of a mad deluded self. In the second part of the play, the roles are reversed. Lady Macbeth became mad, a helpless raving figure who finally commited suicide whereas Macbeth, the tyrant, met his death on the battlefield.