Look at e-spares site, they have a video which gives excellent instructions. However some drum spindles cannot simply be changed by unscrewing the spindle retaining bolts as the video indicates, the spindle is riveted on, but a new spindle can still be fitted if you are prepared to grind the old spindle and rivets off to form a flat to which the new spindle can be bolted to. The holes align. If the new spindle has a raised blip in the centre of the mating surface to stop it laying flat to the drum the centre of the old spindle that is still in the drum can be drilled out until the mating surfaces do lay flat.
Eric
December 2013