OK, I searched this site for the answer to this simple question and kept geeting directed to the manual, which I could not find. Here is the answer, fresh from doing this job twice, first incorrectly and then correctly.
For the record my machine is a 5 hp two stage model 247.886640.
First empty the gas or screw the cap on the tank with a piece of plastic to keep it from leaking. You will need a 3/8" socket driven by either a 1/4" or 3/8" ratchet...prefer the 3/8" drive for more leverage but the 1/4" will do it. Once you have the gas cap sealed remove the 2 self tapping screws from the plastic cover over the pulley area directly in front of the motor. Remove this cover. Then stand the machine up on the auger housing by tipping it forward. It will stand up nicely and expose the bottom. Remove 6 self tapping screwsholding the bottom plate on with the 3/8" socket. Remove the plate and you will see the auger pulley. At the bottom of the pulley there is a spring tensioned friction brake, with a pair of needlenose pliers take the spring off of the screw so the brake comes loose. Looking at the bottom of the machine on the right side there is another spring that pulls the friction plate tight...remove this spring from the bottom edge of the machine so the plate is not held tight. This allows you just enough space to work the old belt off (it it is still there, mine was not) and the new belt up between the plates. Make sure to route the new belt inside the friction brake and onto the large pulley. At this point tip the machine back down so you can see the top of the pulley and the idler wheel and the motor shaft pulley. Your new belt needs to be routed around the large pulley and then inside the idler wheel (back of belt against wheel) and over the motor pulley. To get it over the motor pulley will require a little oomph but I was able to roll it on the pulley by using a pair of channel locks to carefully turn the motor shaft about a 1/4 turn.