Why in America is the title of some of the Harry Potter books changed?

Answer 1

The title was only changed for the first book, Harry Potter and the Philosopher's Stone.

When it was published in the US, the publisher didn't think American children would understand the word philosopher. J.K. Rowling suggested the word "Sorcerer" and it was agreed that sounded more exciting.

Rowling later stated that, had she been in a stronger position at the time she wouldn't have allowed the change.

Answer 2

Only the first one. Apparently, somebody thought that "Philosopher's Stone" would not appeal to an American audience.