new-work Halo cans are adjustable to accommodate different ceiling height. Remove the reflector trim and the lamp. Then remove the three sheet metal screws from near the bottom of the can. Slowly work the can down and out. There is enough slack in the jacketed cable to let the can hang about six inches below the ceiling. Reach through the hole and unclip the face of the junction box to expose the wiring. With power off you should be able to disconnect the 120VAC. If you want to see how these are wired before you pull the can, go to Home Depot and look at a bare new-work fluorescent can. Anyway, look at the armored wires going from the can to the junction box and make sure the ends inside the box are detached, whether you have to cut them or just remove wire nuts. Then take slip joint pliers and squeeze the end of the cable lock to free the armored section from the junction box and remove and discard the can. Buy a new Edison base Halo H-7ICAT assembly and remove the can portion from the frame as described above. You'll have to cut the push connectors off the end of the wires. Strip 5/8" of insulation off the ends of the wires and reinsert throught the hole in the side of the old junction box until the anchor locks. Attach the can wires to 120VAC, bypassing the ballast, which should be completely disconnected. Replace the metal cover on junction box, reinsert can through the ceiling hole, align screw holes, adjust can height to ceiling thickness, and insert screws. If you want, you can push new insulation through the ceiling hole before reinserting the can. You can also caulk the cracks between the ceiling surface and the edge of the can to make it airtight. Once that's done, remove the socket holder and shield inside the can, attach the Edison base LED pigtail that comes in the LED retrofit kits, install the LED kit and you're done.
I've had to install a bunch of these where I had no attic access. Works great and you don't have to cut the ceiling.