Toilet seats are held in place by means of bolts anchored with nuts placed on the underside of the bowl. Because the environment in a bathroom is so damp and humid, nuts made of metal can soon become rusted and stuck. You can remove a toilet seat with stuck nuts in a couple of different ways, depending on whether or not you can loosen the nuts.
Locate the nuts for the toilet seat. They are on the underside of the bowl, just in front of the tank.
Spray the bolts with penetrating lubricant. Allow this to soak in for about 15 minutes.
Loosen the nuts with an adjustable wrench. If you can't grip the nuts with the wrench, use a pair of pliers.
Cut off the stuck bolts, if you cannot remove the screws. Hold a hacksaw blade up to the nut where it meets the underside of the bowl. Saw back and forth, pressing gently, but evenly against the screw. Continue sawing until the nut falls off the screw. Do the same thing for the nut on the other side.
Lift the toilet seat up and off the toilet bowl.