Shut down and unplug everything from the back of your PC.

Flip the power supply switch so that it is OFF.

Take off the side panel by removing the screws that lock it in place.

Your side panel screws will most likely be in different locations than the screws in the picture, depending on your PC case.

Before proceeding, make sure to ground yourself by touching any metal part of the PC case. This releases any built up static charge that could permanently damage your internal parts.