I use this tool, called a fret zapper, to remove frets. The guys at Gruhn Guitars showed me this when I was working there. It’s essentially a 150-watt soldering gun with the tip replaced with two separate pieces of copper.
You simply hold the ends onto the fret and then pull the trigger. The metal acts as a conduit, absorbing a lot of heat very fast, and therefore the fret can be removed much faster than with a standard 80-watt wand-style soldering iron, preserving the fret slots. All it takes is about a second of heat on each fret, and you can safely and cleanly remove an entire set of frets in minutes.
— Dave Johnson, GCA instructor