I can't remember the name of this '80s movie, help?

so, this very popular girl and her friend try to make-over an
unpopular new tudent, but it backfires because she steals the girl's
(girl #1 who is blonde and her friend is black) boyfriend. but the
blonde girl has a stepbrother who is older and out of highschool and
as the movie goes along they fall in love and one night when theyre
helping her dad do something for work they kiss and thats all i
remember. if you could supply a name...

PLEASE. help me!!!