Overheating is caused by inadequate cooling. The most common cause of your problem is dust in the cooling system that is blocking it up.
The only effective cure for this is stripping the laptop apart and cleaning it out with a paint brush.
Some will tell you to use a vacuum cleaner on it, don't, the moving parts in a vacuum cleaner can generate static electricity which can do very serious harm to your laptop. Others will say blow it out with compressed air. Doing this will help but only in the short term as it will blow the dust back into the fan and when you turn it back on the fan will blow most of it back where it was.