This voyage provided a great possiblity for Huck to experience life outside of basic stereotypes. His biggest transformation can be seen through his relationship and interaction with Jim.
In the beginning, he and Tom find fun in pranking on Jim. They view him as an ignorant and simple slave who is strictly property that can be played with.
Throughout the course of the novel, Huck battles a strong internal conflict between Jim as a friend and Jim as property. He has been taught by society that the correct and prudent thing to do would be to turn Jim in (he actually feels like he is stealing from the Widow); however, Huck recognizes Jim as a true friend and is hesitant to rat on a friend. These feelings are further complicated by Jim's talking about buying his wife and freeing his children if he becomes free. Huck questions whether or not he wants to be a part of stealing from people he's never met.
By the end, Huck seems to have accepted Jim as a person. He refers to Jim as the whitest n- he's knows (as close to a compliment as could be expected), he made the decision to help Tom free Jim, and is in awe when Jim sacrifices his freedom to help Tom after Tom was shot.
That's not to say Huck was completely changed though, as he is all set to run away again to avoid the newest attempt to civilize him!