You'll want to power down, unplug the power cord, and press the front panel power button to discharge the capacitors. Next, remove the right side panel and remove the plastic shroud that covers your processors and memory bays. Look closely at the heatsinks on the processors as well as the fans that were covered by the shroud for dust. Dust on the heatsinks and fans will restrict the airflow and cause elevated temperatures. Before you touch anything be sure to touch the metal case frame of the computer to eliminate the chance of an electrostatic discharge (ESD), which can destroy sensitive electronics. Touching the case frame will make your body and the computer have the same electrostatic charge with zero chance of an arc from ESD.
If dust is present, you can use a plastic handle toothbrush and/or mini vacuum, or, a can of canned air (dust remover) available at most department store and electronics shops. Just be very careful with the heatsinks, the metal fins can be easily bent if you use too much force. If you use a can of dust remover, be sure to follow the instructions on the can....holding the can in the improper orientation could cause it to spray liquid which can also be harmful to electronics.