Answer:
At the beginning of the chapters, Amir is shown to largely be selfish and almost purely self-serving. Even after knowing what Hassan went through and supposedly being his friend, Amir thinks that he and Hassan can not be together and that one of them has to leave, showing his selfishness. He then finds a way to get both Hassan and his father, despite his main focus being Hassan, kicked out of the house, even when he knows that Hassan still stood up for him after everything. When he has to flee Afghanistan with his father, Amir begins to really see other people's suffering instead of purely focusing on his own issues. The death of his father also makes Amir see how Baba has used his life to often help people rather than purely himself like Amir often had. All of this leads to Amir accepting Rahim Khan's "way to be good again". After seeing how worse off others had had it in comparison to him, from Hassan to Somaya, and how just a man his father was, he wants to change his ways. Traveling to his homeland again is another sign of Amir's change as he's now possibly putting himself in danger for his friend, rather than purely thinking of his own needs. The news of Hassan's death and true parentage also further pushes Amir as now he can no longer apologize for all that he'd done to Hassan and that he'd done all of this to a blood relative too. This strengthens his resolve to be less selfish and try and help Hassan's son as it's now one of the only things he can do for Hassan. His realization of how Baba had never told them about their blood relation also makes Amir's goals seem more achievable. His father isn't the highly noble figure he'd seemed to be, instead, he was someone like Amir who had made mistakes, yet still tried helping people possibly. Farid and Wahid's comments on what makes a "true Afghan" also show his change as, unlike how he had been in the past while living in Afghanistan, only when he's putting himself on the line on behalf of someone else is he now one. At the end of the nineteenth chapter, Amir's dreams of killing Hassan further shows the guilt he now has over how he treated him. The fact that he later makes sure to leave behind money for the family shows how, through his own guilt and his knowledge of others' struggles in comparison to his own, he is becoming a less selfish and cowardly person.
