This might help with the W clips.
Either I'm just lucky or I have the knack, but I just don't find those clips to be tricky at all. Just remember which way round they go, and they clip on and off easy. Press down and in on one side to remove - you might need something like a flat screwdriver, but usually can be done by hand. Put one side under the rim when replacing, then press in the other side - down and in.Mine is the Adjure unit, from UK supplier but same brand as NField Gear supply.The instruction sheet (scabby photocopy) mentions an "extended bezel trim ring" which is available if there is a gap between the lamp and the rim, but this doesn't apply to the G5 - just the centreing thing as I mentioned. I'm assuming the C5 has the same nacelle...?
The screw on top (12 0 Clock) of the rear rim opens up a clip which holds it all together. Same as the original light. Should be a straight switchover - everything goes back the same way as before. All that's changed is the unit inside.