the headliner fits easily through a door opening.
just remove some trim, the visors, and the dome light. take the headliner out of the car and pull the old material off the foam backing. use 80 grit sand paper (or whatever) to get the foam backing cleaned up.
you can buy new headliner material at any Jo-Ann fabrics store. The grey is a good match (great match actually) and it's cheap.
The best adhesive is Permatex headliner and trim adhesive. Farm and Fleet or Napa have it.
don'ts: don't press the new material on unevenly. if you poke a spot it will have a dent there because the glue will soak in to the new material. if you press it on smooth and even it will look great.
don't get glue on the wrong side of the fabric. it'll ruin it! and although the old fabric may have come off easily, any new fabric will be a nightmare to remove especially with the fresh glue.