The job is pretty simple. Put the trans in neutral, disconnent the wire to the switch, remove the shifter, (be careful to not lose the key or spring), remove the bolts and lift the cover. The switch is retained by a nut on the back side. Be careful not to have any parts laying around that might be knocked into the trans case. You might have a new gasket handy or at least some sealant.
The tricky part is putting the shifter back on with the key and spring. I don't have any tricks to doing this, it just takes some patience. You must hold the spring down, install the key and slide the shifter down on top. Hope this helps.