[HMeeder]

I've taken mine apart (twice) and the only "shade-tree" way I figured was to lay it face down on a nice soft cloth. Using a flat blade screwdriver, pry the edge of the trim ring back, working your way around the tach. Do this carefully, patiently and methodically. By doing it just a bit at a time and making as many as 3 or 4 (or more!) laps around the tach, you can eventually get it to the point where the trim ring will be able to be popped off the housing.

Caution, if you get too aggressive, the trim ring will become dented and cracked along the back. It will dent up some anyways (you'll be cringing during this process) but the rubber spacer rings will hide it when you replace it.

Good Luck!