HOW TO BREAK UP WITH HER AND GOING TO SOMEONE ELSE PLEASE HELP?

okay so im in a 8 month relationship with a girl and just dont feel the same way for her as i once did and i want to break up with her and go out with someone else that goes to the same school but dont want my gf or her friends to do anything to the girl so what to i do iv tryed breaking up with my gf but she just wont exept it and crys and crys and cry and dosent stop bothering me so i took her back and now wondering how to brak up with her also if i just brake up withher for no reason what do i say when she says why did you brak up with me ? also not tell her that im going for someone eles please please pleas help.