Probably caused by the steady accumulation of dust etc meaning cooling is less efficient. Replacing the fans is not for the non-technical as it often means taking the laptop apart to get to the fans themselves. Make sure any inlet area is clear and try raising the laptop up at the rear to get a better through flow of air
You could try clearing the fan blades by using a can of compressed air sold for the purpose of cleaning out electronics and blasting it through the fan inlet and outlet (laptop off at the time!). Using a straw and blowing hard has been known to work but less than ideal as more moisture involved.
Some laptops also have power management software that enables you to change the fan settings (Toshiba do). If it's set to max performance then fans will be switched on more, try setting to lower setting.