It's always a good idea to keep the area you're working on, as clean as possible. In this case, it's a good idea to remove all that gunk, varnish and soil that's around the switch.
1. Remember once you take the faulty switch out, the oil passage is exposed and all that dirt could go inside if the area has not been cleaned before.
2. Remove the oil pressure switch cable if it's still connected.
3. You'll need a socket wrench (22" if I'm not mistaken).....with patience and in a counterclockwise motion take the faulty switch from the engine.
4. In my case I put a drop of new motor oil to the thread on the new oil pressure switch before instalation.
5. Tight by hand first, clockwise, then use the socket wrench to finish the job. No info on necessary torque. Just don't use superhuman strength.
6. Clean the cable and inside the tip that's connected to the new switch and make the connection.
7. Check oil level on the engine. Start the engine, the "Oil" light in the instrument panel should come on for a few second and then come off.
8. Let engine idle for a few seconds and then turn off.
9. Check for leaks.
Note: If the faulty switch seems to be frozen, it's not because is over tight, most likely is due to the time is been sitting in that area.....patience, it will come out.