The fans in a laptop are integral to cooling its internal components. The fans work by drawing cooler air from the outside of the case and running it over the heated components such as the random access memory or central processor. Over time, dust builds up on the fan blades. This leads to degraded airflow. If you don't clean the fan periodically, the components will overheat. A popular method for cleaning fans is by using compressed air, however this method can blow dust into the laptop rather than sucking it out, leading to further overheating.
Power off the laptop and remove the battery.
Locate any vents on the outside of the laptop.
Stick a small wooden skewer through the vent to prevent the fan blades from spinning while you work on the fan.
Use tweezers to pry out any large particulates on the fan.
Use a hand vacuum cleaner, or a vacuum cleaner attachment to remove any dust particles from the fan.
Remove the wooden skewer from the vent and turn the laptop on. The rest of the dust should blow out of the vent once you start the laptop.