Removal of under seat 5 1/4 woofer fixture

I want to upgrade my rear 5 1/4" Woofers on my 1992 Daimler. To get more space I would like to remove the woofer-fixture without destroying it. It seems to be fixed with 3 clips but I cant get them loose. Any idears - anyone?

3 clips holding the woofer frame - how can I remove the woofer frame?

Well, it wasn’t too complicated. The metal clips have a stair-step shape and should be pressed against the center while prying out the frame.