How do Lady Macbeth and the witches influence Macbeth to change?

The Weird Sisters influence Macbeth to change simply by telling him that he will become Thane of Cawdor and then king. When he learns he has been made the Thane of Cawdor, Macbeth begins to hope for the throne in a way that he seems never to have done before. Judging by the captain's description of him in battle, Macbeth has been loyal and brave, a good subject and kinsman to King Duncan. Once the witches plant the seed of ambition, it begins to grow out of control, prompting Macbeth to dream of killing Duncan—and possibly his son, Malcolm—prior even to returning home to the company of his murderous wife.
Lady Macbeth influences her husband to change by persuading him to go forward with their plan, even after he decides they would "proceed no further in this business" (Act I, Scene 7, line 32). Lady Macbeth insults her husband's masculinity, convincing him he will not be a man if he does not keep his promise to her and take the throne now. After he does commit the murder, she insists that his guilt makes him a coward. Soon enough, she realizes she's created a monster who is even capable of killing innocent women and children without a second thought.