OK, I have done this several times. And it is easier than you think. First remove the top: remove screws and turn the round nut on the film advance lever normally (ie, counterclockwise to loosen). After the top is off you CAREFULLY wipe all the glass surfaces with a soft, clean tissue impregnated with water with a bit of dish liquid. Contrary to caveats (elekm) about not wiping the sliver coated mirror, you can wipe it with this solution. Do not use alcohol on that mirror, however. The solution for this cleaning has to have enough dish liquid to create a non static environment but not so much that it leaves a residue.
Of course, you are having to get into tiny crevices here. Take your time. What I do is cut small pieces of tissue beforehand and fold a few times. Then grasp into a tweezer and carefully wipe the surfaces. Immediately thereafter, before fully dried, I use a new tissue, again in tweezers, to fully dry what I have just washed. CAREFUL is the byword here. It really is as easy as I just described. - David Lyga