How to replace a toilet seat in your bathroom
A toilet seat is held to the bowl with two bolts. On some, the top of the bolt is attached to the hinges for the seat and cover, the nuts on older toilet seats are sometimes difficult to reach; a socket wrench usually works best.
Sometimes pliers can grip the nut, but if it is corroded they may not be able to turn it.
In this case, squirt penetrating oil on the bolt and loosen it. If this does work, the bolt will have to be cut with a hacksaw.
Cut it above the washer on the top of the bowl. Cover the ceramic bowl with cardboard or plywood so the surface is not damage.
New toilet seats have plastic hinges. These have a plastic screw that can be easily reached from the top and a plastic nut. A screwdriver and pliers will tighten and loosen these easily.
The new seat will come with all the parts necessary for installation, which eliminates the corrosion problem. Insert the bolts in the holes and tighten the nuts from underneath. Do not over tighten them.