Very simple. Pull the bolt out of your secondary with a 9/16" socket. Along with it will come a coupler with a o-ring and shim washers on it. Stick it in a drawer. You won't need them anymore. Now thread the new part in Counter-clockwise (left hand threads) until you get the belt defection you want and tighten the new bolt they give you with the allen wrench they give you. Adjust the belt deflection so your sled track barely turns when hung from the rafters or your belt squeals a little or sled creeps just a hair if sitting on the ground. That will put you where you need to be. Whenever you need to adjust it, just be sure to loosen the center bolt you put in a little, adjust it and retighten. Keep the allen wrench on board. Good luck!
Aaron