Hello Ive Been With My Gf For A Year Now But I Kinda Like This Girl From My School What Do I Do?

Don't just dump her like a douche. Just tell her, "I know we've been dating for a year, and ((I don't know so if I'm wrong... opps.)) nothing has gone wrong but. We're still young and well I just don't feel the same way I did in the beginning. I'm sorry. I hope you understand." A bit forward but gentle. If she doesn't get it then tell her, "I'm sorry but we're over." Don't say let's still be friends because that will make her believe she might still have a chance. An don't be afraid. You can do it! :D