I'm not familiar with these specific speakers/housings, but I did spend 10 years in the car audio business. My educated guess would be that the metal mesh pops out. Best thing to use is a 90 degree angles pick. Be careful though. It's very easy to distort the grille. Once that is off, you should be able to determine how the speakers are held on. Again, I have no personal experience with these specific speakers, so take my advice with a grain of salt.
Two wrongs don't make a right, but three rights make a left.