16. Time to get back to the CPU. It is highly advisable to remove the rest of the old paste before applying a new dose. Carefully wipe the bulk of it away with a clean piece of cloth.
17. Next, take another piece of cloth and slightly moisten it with pure or rubbing alcohol (at least 70%+). Gently sweep the surface of the CPU with it a couple of times to remove all residues. Take care not to accidentally touch the surface, as this will likely leave greasy fingerprints.
18. Apply a tiny dose of fresh thermal paste - a bit smaller than the size of a pea - on top of your CPU and evenly spread it with the help a a strong sheet of paper (business cards will do). The idea is to thoroughly cover the whole surface while keeping the layer as thin as possible to ensure ideal cooling conditions.
19. If present, make sure to remove the plastic foliage covering the underside of your CPU cooler. Again, try not to accidentally touch the metal surface with your fingers after doing so.
20. Put all necessary backplate screws in place and rotate the cooler until it matches their position. Gently lower it onto the CPU, ideally without twisting it around too much once it is has made contact. Tighten the screws connecting the cooler to the backplate/motherboard.
21. Once the cooler is firmly connected to the motherboard, make sure it pushes the air out of the rear of your PC case to optimize airflow (whether you place the fan before or behind the heatsink is up to your model and preference).
22. As a final step, put your motherboard back into the PC case and reattach all necessary screws as well as the cables and PCI cards that you previously removed. Don't forget to connect the fan power plug to the 4-pin connector on the motherboard before closing it up again.
Testing your new setup
If everything has gone according to plan, your new and improved PC is set to go. Power it up and you will likely soon notice a significant reduction of fan noise. To check if the new setup remains stable ready under a high performance level, you should put it under a stress test. Download Prime95 as well as SpeedFan to give your CPU something intensive to work on while measuring its peak temperature.
Open both programs and trigger a testing routine under Prime95. After about 3 minutes, the temperature should start to flatten out (if it goes as high as 90°C or more, cancel the test, as something has likely gone wrong during the installation). Note the results and exit Prime95 by closing it from the taskbar.
This might also be of interest: How to benchmark your PC for free
Its a good idea to compare the final temperature with similar hardware setups from the internet to see if your cooler can compete with general standards. As a rule of thumb however, anything below 70°C is fine and anything under 60°C is quite good.
Note: Prime95 is one of the most intensive stress tests that are available for CPUs and will push them well beyond everyday boundaries. Thus, don't worry if your new fan starts to make itself fairly audible during the test, as your PC won't have to deal with comparable workloads in everyday settings and will likely stay much quieter – even while gaming.