It might be hard to accept, but the girl already has a boyfriend and trying to get her to like you would not be the right thing to do. The only advice I can give you is to become friends, nothing more, with her. After all, she may not be with this boyfriend much longer and if you are already friends when the relationship ends with her boyfriend, you may have a better chance of being with her afterwards. After all, you'll be the person she can rely on or the "shoulder to cry on" as she deals with the pain of the break up.
Then she has to choose you or her boyfriend.
Does the girl know you like her? How long have you an and your boyfriend been together? And are you asking what should you do?
Try an show her how cool you are compared to her boyfriend
If he is her boyfriend, hopefully, she would like him.
Wait till she doesn't have a boyfriend or move on
Treat her better than her boyfriend does.
You get beat up
Find a way to impress her.
It means that they like you more then they like there boyfriend
fight the other kid and take the girl
Move on, she's taken.
you make a girl jealous and the girl will hate her boyfriend and follow you as her boyfriend and listen to that song Justin bieber one time