It is basically held in by all the fittings.
You need to remove the interior lamp, and its surround, both sun visors, the handles above the doors, or blanking plates, and whatever is above the rear side windows. There are probably some buttons along the back edge. These need care and swearing to remove, a warm day helps.
It may sit behind some of the side trims on the pillars, so they may need removal too.
Once all that lot is off, and the tears are dry, the roofliner should drop down. It may however have some glue spots on it, so some gentle easing may be required. If you bend/kink the fibreboard, repairing that will be very difficult.
Then you manoeuvre it out of the rear hatch, and try to carry it without it folding in half, while wondering where to put it. Clear a space somewhere first. If you intend to play with glue on the lounge floor, might need a groundsheet to avoid a divorce.