If your looking to jump higher you need to jump more. I was a ball player and was able to dunk also depspite me being short. I found that simply going out and jumping worked for me. Sometimes I added weights to my ankles. Honestly if you can just barely dunk you can probably get a little more than your palm over the rim so gauge your improvements by how much higher you are able to get from your prior jumps. Working your calves, quads, and glutes in the weight room should help too. Just becareful with the amount of weight you gain from weght training. I cant even come close to dunking anymore but thats what 50 to 60lbs from years of body building will do to you.