Usually all 'back to the wall' type toilet seats are fitted from the top for the obvious reason when in position a standard fitting toilet seat fixings can't be accessed without removing the pan.
Most top fitted are accessed by popping up the top cover cap to reveal a nut and expansion bolt undo the nut each side the seat comes off new seat new bolt but ensure the fixings are 'top fitting for back to wall toilet pan.
bob, September 2013
