Why do you want to change the fan speed?
The fan speed is controlled according to the temperature detected by the thermal sensors mounted on or very near the CPU. If this is not keeping your temperature in a safe operating temperature you will need to determine what is causing the computer to overheat. A build up of dust, particularly in the heatsink and fan assembly on the CPU, can cause this. If this is the case then trying to ramp up the fan speed probably will not be effective.
Please download and install Speccy
to provide us with information about your computer. Clicking on this link will automatically initiate the download.
When Speccy opens you will see a screen similar to the one below.
Click on File which is outlined in red in the screen above, and then click on Publish Snapshot.
The following screen will appear, click on Yes.
The following screen will appear, click on Copy to Clipboard.
In your next post right click inside the Reply to Topic box, then click on Paste. This will load a link to the Speccy log.