The original mount is disassembled by removing the four longer screws. You can see which screws you need to remove from the photo. This will remove the mount together with the spacer ring incl. aperture lever. The aperture selection ring will remain on the lens, but be no longer fixed. Beneath it is a small spring loaded ball for the click stops. Be careful not to remove the aperture ring to avoid losing the little ball. I found it necessary to also disassemble the mount/spacer construction to be better able to transfer the hole positions onto the M42 adapter in the next step. If you disassemble the mount/spacer assembly be careful because there are a couple of small ball bearings inside.