I replaced all of my lenses and rebed all of my hatches this spring.  I also repainted that plastic frame - looks like new again.  To remove the plastic inner frame, take the screws out of the screen retainer clips (4 of them I believe). You have to pry off the little caps hiding the screw heads with a razor blade. The frame will come right out.  It is possible that there might be some velcro holding it to the ceiling, but the screws are for sure.  

On the top side, remove all of the screws holding the aluminum hatch frame to the deck.  Get a can of Debond Marine Formula and spray all of the sealant you can see.  Spray it all around the frame and into the screw holes.  Go get a cup of coffee for 20 minutes or so and come back.  The spray breaks the adhesive bond of the sealant.  You can take a putty knife and a flat head screw driver and start prying under the frame.  It will come out pretty easily once you get it started.  Once out, use the Debond spray to remove all of the old sealant from the hatch frame and the deck.  You will probably notice (like I did on ALL of my hatches) that the plywood core is exposed at the hatch openings.  You will also see significant gaps between the ceiling layer and the plywood core.  Now is the time to mix up some thickened epoxy and seal these openings and the core.  In my case, the main hatch over the salon table seems to have been leaking since the day it was made, and water had been slowly infiltrating the plywood core for years, rolling downhill internally to the port side.  The annoying drips from the dorade vent opening in the ceiling, the light fixture over the stove, and elsewhere on the port side of the cabin were all due to this water penetrating the core at my main hatch (because the leaks stopped when I epoxied the hatch opening).  Anyway, the epoxy job is made much easier by pressing on little sheets of wax paper all around the opening after you goop on all of the thickened epoxy (the sheets press the epoxy flat and will not stick to it).  This greatly reduces the amount of sanding you will need to do by about 95%.  Clean up the deck surface where the sealant will be with some Acetone and a rag to remove any residuals from the sealant and Debond.

When you go to reinstall the hatch, tape all around the frame area on the deck.  Do not be shy with the sealant.  Put way too much on and let it ooze out onto the tape.  Wipe it up with your finger.  Let it set for 15 minutes or so, and then remove the masking tape.  My first attempt on a couple of my hatches had to be redone because I was skimpy with the sealant.  Learn from my mistakes.  

I have attached a couple of photos that may help.  

Thanks,
Don