Speaker removal 1998 V70

I have a faulty speaker in the driver's door of a 98 V70 and want to remove and replace it. It is mounted in a plastic frame. The frame is fastened to the door with one torx screw and two red plastic "screws" of some sort. I've removed the torx screw but am quite unable to remove the red plastic screws. The heads are slotted. I've turned them 90 degrees with the thought that they would release, but they don't. I've tryed some gentle prying but they still won't release. I am concerned that any additional force might break something. Am I missing something obvious? Can anyone tell me how to get these off? Any advice much appreciated.