RE: Changing draw length on HC Excalibur
While I don't know anything specific about that bow, I'm assuming it's of the single cam variety (idler wheel on top).
All you usually have to do to adjust draw length on most single cams is to remove the cam, loosen a couple of screws and shift the two parts of the cam slightly. You then replace the screws. If you look closely at the cam, you will probably notice that there are a few small screws holding two pieces of it together.
If you don't have a manual for the bow, you may be best off taking it to a pro shop and paying them the few dollars to set it up for your uses.
Good luck and enjoy the bow!