how do i replace the belt on a hoover windtunnel vacuum?

i have a hoover windtunnel mach 6.9 (upright). i bought the right belt (i took the broken one with me) but it appears to have TWO belts on the roller -- a skinny one that is intact, and the fat one that broke. i don't know if the broken belt goes OVER the skinny belt, beside the skinny belt (it doesn't look like it fits that way--no groove, or UNDER the skinny belt. or if the skinny belt shouldn't be there at all. AND there's a little wheel between the main axle that the skinny belt is looped around and the roller. i don't know if any or either belt should be looped around this inner little wheel or if one or both run between the main axle wheel & the little wheel. Please help--i'm up to my nostrils in dust! thanks, nancy