If you search the SL Forum, there are probably more detailed instructions there. Maybe even one with pictures. The basics are:
Put both hands on the rear view mirror and pull down hard. It's held in by a spring clip. This exposes a mount that has, I think, 3 screws that you remove. I don't believe the '74 has an interior light on the trim panel, but if for some reason you do, you need to pull the light out and unplug it. I think you also have to remove the female piece that the visor clip fits into. It's held in by a phillips screw. There's also a hidden screw on the trim piece near the visor mount. You can't see the screw, but insert a medium phillips screwdriver in the hole and remove the screw. At this point, you should be able to remove the trim piece. Some have some type of sealant on the windshield side. If your's does, just try not to make a mess. After you get the trim piece off, removing the visor becomes obvious.
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino