Spiker on here whould be able to help. He's done it before with another poster.
The module you have to change has two screws holding it to the cam. You remove them and the mod will just about fall out. You really need to physically measure the draw length to determine just what it is. Draw mods are numbered and one number less means 1" less. So if you want to decrease the draw length by 2" then you need #5 modules.
Before you go loking for mods you need to know just which ones you need. There were Sonic wheels and Ultrasonic wheels and they use different modules. Spiker should be able to tell you which are which. As to where to buy them? Classified ads on www.archerytalk.com or EBay.
If You're Not Living on the Edge You're Taking Up Too Much Space
Martin/Rytera Staff Shooter
PSAA Life member, UBP Life member
PADI AOW Diver