It was originally released simply as "Star Wars". Only after its completely unanticipated commercial success (and nomination for Best Picture, but losing out to an absolutely horrid "Annie Hall"), that Lucas signed on the main cast members to do two more films and then re-released the original with a retitled "Star Wars: Episode IV - A New Hope".
If I remember right, it always said Episode IV in the opening crawl thingy.
No sir, the title has ALWAYS been Episode 4, A NEW HOPE.
The original theatrical release said "Episode IV" right above all the text in the beginning that explained the background of the story. I remember it distinctly; when I first saw the the original in the theater as a kid, I was quite puzzled: "What's this Episode IV business? There's no other episodes!"