How might a character change in the course of a novel

Depends on what goes on in the novel for example,

War: They might start innocent go to war and as the war goes on the blood shed the death changes him into a cold hearted person.

Romance: They start awkward and then evolve to be more social and fall in love with (*Secondary*)

The experiences they undergo during the story alter their perception of the world, of other characters, and of themselves. The world is changing around them and they need to adapt. They travel to a new world and need to adapt to it. They're growing older.