If your at your maximum, try this exercise with your present bow: pull it back 12" (pause), continue to 18" (pause), continue to full draw (pause), then down to 18" (pause), then to 12" (pause) before letting it down.
Repeat three times, then switch to left hand and do it again. If it is difficult to do this exercise from both sides (Right & Left), then you are probably at your maximum. If you work at this exercise until it is easy, you will be ready to move up 5 lbs. You should do this exercise every other day for several weeks. Do the exercises if your not shooting to stay in condition.
If you shoot 50# comfortably, and can pull 55# but not 60#, this exercise will help if your going to move up in weight.