I think you're either born with intelligence or you're not...but it can be worked on to some extent. A person can improve their brain's power with puzzles and the like, but it will only let them access their full potential, not make them mroe inelligent.
To clarify also, Knowledge does not equal intelligence, and vice versa. I've known people who were extremly knowledgable, but idf you asked them anything outside of their field of study, they couldn't even comprehend the question.
Likewise, I've known intelligent peoplem who simply don't know things, due to either an old educational system, or a bad one.