Hi! To replace a spiro pipe without damaging the ceiling, it's best to work from the attic. Unscrew the ventilation grille at the bottom, loosen the old pipe at the top, pull it out, and insert a new one, be sure to have thermal insulation to avoid condensation. Don't turn off the vent—it should operate freely. Also, check the mushroom valve on the roof to make sure it's watertight.