Turn my friend into my girlfriend ?

Allright there is this girl that I really liked since like the 5th grade (im in 9th now.) So basically.... in 5th grade we were friends, were together for part of sixth grade, friends for 7th, and friends for eigth. Well, now its high school, and guess what, I LIKE HER AGAIN. So here's the deal i have no clue what to do (should i tell her or have we been friends for too long?) Also if I tell her, should I do it at the mixer coming up or somewhere else? I really would appreciate all feedback, and if ur a girl teel me howd you like to be approached (if at all)