Why do you think the narrator wants to change Doodle?
Brother, the narrator, notes that Doodle is a disappointment. Doodle is born deformed and the narrator describes it like this, "He seemed all head, with a tiny body which was red and shriveled like an old man's." The narrator is six years old at the time. He loves to be very active outside. So, he hopes that when Doodle is older (if he survives), that he and Doodle will be able to do these things together. Doodle surprises everyone's expectations by surviving and being mentally active. But the narrator is not satisfied. His parents encourage him to take Doodle with him everywhere he goes, and the narrator feels like Doodle is a burden.
When Doodle is five years old, and the narrator is eleven, the narrator notes that he is embarrassed to have an invalid brother. So, this is why the narrator begins teaching Doodle to walk. When he and Doodle present their progress to their parents, everyone is overjoyed. However, the narrator is crying because he knows he hasn't taught Doodle out of generosity; he's done it out of embarrassment and pride:
They did not know that I did it for myself, that pride, whose slave I was, spoke to me louder than all their voices, and that Doodle walked only because I was ashamed of having a crippled brother.
Brother cares enough to feel ashamed about his motives, but this doesn't stop him from continuing to push Doodle to be more "normal."