I'm going to presume that you mean the one on the brake pedal.
Become a pretzel.
No. Seriously, it's not easy to get to, even for someone that's small. My reference material simply states: If the switch fails this test, replace it and gives no procedure for it. The picture leads me to believe that it is simply clipped to the pedal and bracket. But it could also be that those clips have bolts to secure them.
If this is the baby we're talking about, it simply clips in and out.
Disconnecting the harness at that angle isn't going to be easy. Be patient, use a few choice cusswords to convince it you're stronger and better (make sure no young ears are around first) and wiggle up and down and back and forth as you pull.
One of my other references shows it as a switch that's threaded into a bracket and has only two wires going to it. That's much easier: Pop the connector out and screw the old switch out.
Installation of the new part, whichever it is, is the exact opposite.