How does Huck change his mind about Tom?as a novel as a whole

Tom simply loses his credibility gradually  in the eyes of Huck, who had already begun forming his own views about people in general. The one thing that is consistent with Huck is that he believes people and makes generalizations of people quite fast only to realize later how phony, false, and hypocritical people can be.

Tom is a much more privileged child than Huck and most of his adventures are in his imagination. He makes much of nothing and creates stories. As expected, Huck hung by every word Tom said, and considered himself a special part of Tom's gang. However, the failure to complete tasks and the failed attempts to do the many different robberies and things that Tom wanted to plan made Huck realize that Tom was just full of it and slowly began to see him in a different light.