It often has to do with dust (Fans are usually the most likely culprit). Cleaning your laptop is a good idea, if you are not comfortable doing it yourself, most computer repair shops will do it for a small fee.
Note, if you do it yourself, do it on a hard surface (not around carpets or rugs), if possible not on a dry day. Remove the battery before opening the laptop. And use compressed air only, do not use any chemicals or solvents inside the computer.
If you lookup the model, often you can find detailed explanations of how to disassemble a laptop. As they all have different tricks to them.