I'm a girl, i'm 14 and i would like to turn jewish, how can i do that?

I recommend you research Judaism, and you can start on the web with "Converting to Judaism". I am not Jewish, but I researched it some. I realized I needed to remain Christian. Learn as much as you can about the Jewish faith, and which type of Judaism would be best for you. (for example, I don't believe you would be accepted in the Orthodox faith). I wish you well.