How can i convince my dad to let my buy a new guitar?

Well, first try calmly explaining to him how much you love playing guitar and that you may be able to take your skills somewhere one day, but you can't do that if you don't have a good guitar to practice on! If that doesn't work, just do it anyways. It's the sweet joy of teenaged rebellion that can get one places in life that parents formerly wouldn't allow, but eventually be proud of.