Clean the Case
1. Power down the computer and remove all cables.
2. Open the case by removing the screws on the back. There's usually four, but your PC may have more or less.

3. Hold the compressed air can upright and squeeze the trigger to blow the dust from the case. Only squeeze in shorts bursts, do no not tilt the can and make sure to aim so that the dust is blowing out of the case rather than in.
4. Wipe down any vent holes that are covered in dust, such as the back or sides where the fans blow. If the fans are dusty, hold them steady with one finger while wiping gently. Clean all dusty areas within the case thoroughly.
5. Remove the memory and reseat it while pressing evenly on both ends. Do the same with the video card, then close up the PC case.
Replace the Memory
6. Download the Crucial Memory Scanner (see Resources) and let it analyze your system. When finished, it will tell you how many memory sticks you have installed and the specific type. Write it down or print the results.
7. Purchase memory identical to the type installed in your system or go to a higher capacity. The Crucial Scanner will show you the maximum upgrade available.
8. Hold onto a metal object and release the two white latches that secure the memory. Touching a metal object will discharge harmful static electricity and prevent it from zapping your computer.
9. Open and remove the memory as instructed under 'Clean the Case.'
10. Replace it with the new sticks, making sure to snap them in firmly. Both sides will 'click' when installed properly.