Remove the 4 screws that secure the top cover at the back of the system unit.
Hold both sides of the system unit cover and push it backward about 25 mm.
Lift the top cover up to remove it completely.
Touch the bare metal frame of your system unit to dissipate the static electricity from your body. Do not touch any of the components inside the frame before you touch the frame. Do not touch any of the components that have a voltage warning label.