The retainer is a left-hand thread and there is a flat on the motor shaft to assist in holding it still whilst your unscrew.
Remove the idler wheel assembly and with all the screws off the back panel, ease out the drum just enough to get the old belt off. Fit new belt and get it on to the motor shaft pulley.
Refit the idler and spring then refit panel screws.
Ken Doerr
February 2007