At the sunroof opening, pull up the weatherstripping to expose the glued edge of the headliner. The vinyl will pull off at the glue joint. Clean off any remaining glue or vinyl bits to ready the surface for the new headliner, which will also be glued here. Then you should be able to remove the headliner as one big piece through the hatch or door openings. Take a minute to clean the bare metal roof and re-glue any insulation stuck to the roof that may have come loose.