Jonas is the only character who really changes in The Giver, because he finds out the truth about his community and decides to do something about it.
Since The Giver takes place in a community where everything is tightly controlled and most decisions are made for people, most characters do not undergo any change throughout the course of the book. The life they have is all they know, so it never occurs to them that life could have color or emotion.
At the beginning of the book, Jonas is just as obedient and unquestioning as everyone else. When he is told to do something, he does it immediately.
Instantly, obediently, Jonas had dropped his bike on its side on the path behind his family's dwelling. He had run indoors and stayed there, alone. (P. 2)
Jonas’s obedience continues as he gets older, but he begins to notice he is different. The first example of this is when he is playing catch with his friend Asher and he notices something unique about the apple.
[This] was the part that he couldn't adequately understand—the apple had changed. Just for an instant. It had changed in mid-air, he remembered. (p. 24)
It is because of Jonas’s ability to see color—cold the capacity to see beyond by the community—begins to set him apart from other people in his community. It is for this reason that he is chosen as the community’s Receiver of Memory.
Being the Receiver of Memory gives Jonas special privileges. He no longer has to follow all of the rules. He finds out about the past. He begins to realize that no one in the community feels pain, but they also don’t feel love, happiness, or any other powerful emotion.
Jonas’s biggest change is when he sees his father kill a newborn baby, because the baby is a twin and they can’t have to identical people around because it would be confusing. Jonas is horrified, and he suddenly understands what is really going on in the community.
The Giver gave a rueful, anguished, empty laugh. "Jonas, you and I are the only ones who have feelings. We've been sharing them now for almost a year." (p. 154)
This is when Jonas decides to leave the community with Jonas. He and The Giver form a plan. Jonas has changed from an obedient, ignorant child to an empathetic, intelligent young man.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.