It depends on the style. If you have the metal mesh style, you can either grind off the plastic welds with a dremel or use a soldering iron and melt them off. If you have the all plastic version, then you'll need something to cut the grille off. I'd probably use a dremel with a spiral cutting bit.
The "grills" on my 2002 were not pre-molded and welded to the door, rather it was all one piece. I tried a dremel on one side, but it would do that spastic buzz and take a little more than I wanted every now and then. On the other panel, I went OG ghetto style and used a steak knife. It cut surprisingly well, and was easy to control. A light once over with some sandpaper and it was done deal.