I would open it up and clean out the fans. According to how dirty it is you may need to get to the heat sink clean out the vent ports and reapply thermal paste. To see if we have a guide on your machine please give us the model name and number. Here's the thermal paste I use: Arctic Silver Thermal Paste
3.5 gram Arctic Silver thermal paste tube. Thermal paste forms a continuous, conductive layer between a processor and its head sink, improving cooling performance and keeping your important chips from overheating. Whenever you remove a heat sink, it's ver — 50+ available at 8.95 each.