My oil pressure switch is leaking - what's involved in changing it? Is there enuff room to change it from under the car?

 

jack the car up and support it on axle stands, climb underneath, unplug the wiring from the switch, then unscrew the switch, refit in reverse order, job sorted.

You may possibly be able to replace it by reaching around the inlet without jacking the car up.

 

As above mate, dead cheap to buy also.