How did Two Bit change throughout the book?
I do not think that Two-Bit is a super dynamic character. That doesn't mean that I think he doesn't change at all, but I don't think he changes all that much. Part of my reason for thinking that way is because Two-Bit is not a central character to the story line. He's important, but much less so compared to Ponyboy, Cherry, or Johnny.
Two-Bit provides the comic relief for the gang. He's always full of energy, and his quick wit is always ready to give some smart retort. For that reason, he tends to come across as childish and immature at times. But by the end of the story, he has seen two of his close friends die. Because of that, his happy go lucky tendencies have faded, and Two-Bit has become more serious about life in general.