“The earliest evidence for quotes of this type comes from the "Love Project", an initiative begun at 1970 at a high school in Brooklyn, New York by teacher Arleen Lorrance. According to the project's website, "Be the change you want to see happen, instead of trying to change anyone else" was one of the principles of the Project "received" by Lorrance in 1970 -- but contemporaneous evidence for this has not been found.”

Source: Wikiquote