This will get you into the Power Supply - Even if it's unplugged, there could be charged capacitors in here! You can skip this step to continue with the guide.

Remove Two Back screws - These are 3x6mm Black Machine Screws

Remove the 6 - 3x11mm Plastic Tapping Screws

If you want to clean the fan, there's 2 - 30mm Plastic Tapping screws holding it in.