Without looking at the bow but doing a bit of searching, it appears that draw length is adjusted by attaching the cables to different positions on the tiller wheels. It would be wise to get a copy of the manual if you can and take it to an archery shop to do the adjustment (you will need a bow press).
Also, the 2216 arrows you are shooting are awfully heavy. Great for penetration but not to good for any speed. Especially out of that old design. Don't get me wrong. Your bow is still very capable of killing deer as you've proved. But it isn't even close to matching today's top of the line bow speeds.
Carbon arrow will give you about 20 FPS more speed (1 fps per 5 grains is a rough estimate) but you have to be careful you do not go too light. I believe Bear recommended no less than 7 gr per pound of draw weight.