When I removed mine (so it could be wrapped) I found you have to remove the whole trim piece that it sits in. This is easy IF you have a trim removal lever (the hard plastic type - I guess you could use a screwdriver wrapped in tape or something). Prise the trim piece upwards, it just pops out. Then you unclip a little cable and can take the whole piece indoors. The ashtray screws are obvious once you have it in front of you.
I think there's a guide in the DIY section on here.