First off Height is not everything it just makes reaching the rim easier. You need to understand on what muscles make you jump. It is not only the legs, it is also your core otherwise know as the ab area. Then after you workout your core you need to work out legs. These muscles are calfs, hamstrings, quads. Go to your local gym and look for machines that work out these muscles. Do these excerise's till you cant feel your legs. You will get a burning feeling while doing them but dont worry that means muscle is building. Im 5'10 and i only need 3.5 inches till i could touch rim and this is after 3 weeks of training. Keep working on it and you could become superman yourself.