Can you post a picture of the pedestal post? I am not sure what you mean that they won't rise or lower. Is the height adjustable? The actual seat to pedestal connection is slip on using a plastic bushing. The base mount of the seat 'clamp' is a sleeve that can be tightened by turning a knob. The shaft connected to the know is usually threaded and when you turn it the split collar tightens or loosens. The threads may be frozen, Use a penetrant, maybe several times over a few days to see if the screw can be turned. Try a vice grip on the shaft. If you try to wrench off the knob, it will break. The entire seat and base can be slid up and off the pedestal but without loosening the knob, that can be hard to do. Try spraying penetrant around the circumference of the seat base and tap it upwards with a hammer and maybe a block of wood. That seat clamp should be the easiest ti free up. The seat clamp, slider knob or rod if present may be much harder. If the pedestal is adjustable in height, that may also be tough to free up. Heat can help, just be careful.