You may need to change cpu fan speed due to many reasons like troublesome computer sound, the machine running slowly and many such reasons. If your machine is running for many years and requires a clean re installing, registry cleaning, having the problem of low space on hard drives, viruses and so on; you will need to change cpu fan speed also.

You may need to change cpu fan speed if the speed of a cooler has become slow. If the fan is working slowly, your computer will be working but slowly as well. The modern CPUs have the technology of in built temperature control function, thus allowing them to provide perfect functionality with dropping the performance to low temperature. Moreover, the motherboard allows the CPU to heat up to some particular temperature around 70C. This temperature is pretty high but it’s not much for a CPU to keep working.

If you see that your computer is running slowly, one probable reason can be the speed of the CPU fan. Check the CPU temperature and fan speed. You can change cpu fan speed in two particular ways. Firstly, by using some applications, which are available with the motherboard of the computer and the other easier way is by looking for the system BIOS (Basic Input Output System). You can also enter the BIOS by pressing "F2" or "Del" keys according to the type of BIOS you have. Next, you will see a message while starting or restarting the computer. The message will stay for a short time on the bottom of the screen before the OS starts to load. The BIOS screen gives detailed information about the fan rotation speed, current CPU temperature, and other vital information. Concentrate on the fan speed and the temperature of the CPU. Keep in mind that one is connected with the other. The CPU fan should be working in steady connection and around 4500 rpm.

If you see that the CPU temperature is around 60C and the CPU fan speed is much low than 4000 rpm, you will have to replace the fan itself. If the fan speed is much less than normal or not even steady and fluctuates rapidly between comparatively high and low speeds, you need to change the settings also. An improper CPU fan can make the computer shut down suddenly and keeping the fan speed perfect is also one of the motherboard's safety measures. Thus, try and analyze the need and importance before changing a CPU fan speed.