A computer processor gives off a good deal of heat. When the internal temperature of a computer begins to rise, you run the risk of the processor getting fried, which will destroy your computer. To combat this, computer manufacturers have placed fans inside to keep them cool. Like any mechanical part, however, a fan can malfunction and must be replaced as soon as possible.
Turn off the computer. Remove the power cord and all cables.
Unplug the fan power cable from the computer. Unscrew the old fan from the side of the computer case and keep the screws in a secure location.