According to my old Kenmore manual (mine was a model #86880100), there's a "Type A" and a "Type B" assembly, but the basic steps are pretty common to both. You need to
1) Unplug/de-energize.
2) Lift & prop the top securely (use a putty knife to pry it up/release the clips holding the top to the cabinet front that are about 2" in from the sides w/o damaging the paint).
2a) - - unscrew the two screws attaching the lint trap opening to the lint trap chute.
3) Remove the front panel (sheetmetal screws as I recall).
4) Relieve pressure on the belt by pushing idler pulley towards motor (note: pinch hazard).
5) Remove belt with your other hand. Note that you shouldn't have to remove the drum to do this.
6. Reverse procedure.
While you're in that far, check the drum support rolller(s), make sure they are solid (look for signs of wear - metal shavings or play in the rollers, may also make noise during operation). If there's slop in them, they will cause excessive strain on the belt and it will fail prematurely.
Replacing them involves removal of the drum, but it makes more sense to do this now than do it over later.
You might be able to download a current PDF of the manual - - I'm giving you the abbreviated version, don't have time to re-write the book.
Good luck, | 
