Flipping the lens around, remove the three marked screws to remove the lens bayonet mount.

The housing of the aperture lever can now be removed as well. The lever has to come up through gap shown the metal ring, marked in green.

The three screws marked in orange can now be removed. USE CAUTION WHEN HANDLING THE APERTURE RING FROM HERE ON!

The aperture ring is now loose, and the small ball bearing the provides the detent is spring loaded and WILL fly off on you if precautions are not taken.