Step 8: Remove old fan
If the fan is connected via a header on the PCB, you can simply unplug it and plug in the new fan. In my case it was soldered directly. If this is the case, make sure you get the same type of connector for the new fan.
If the fan is soldered, you have two options - cut mid-wire, join and insulate, or, as I decided to do, unsolder from the PCB and solder the new fan directly. This is slightly more trouble but the result looked better.
If you decide to unsolder the fan, first remove the power supply PCB from the case. This is attached via several screws. It is best to move it as little as possible, because of the dozens of wires connected. Moving unnecessarily will probably result in broken wires, which will be extremely hard to find. I moved the PCB only enough to remove and replace the fan.
Another advantage of this is, you are unlikely to touch the high voltage area of the PCB.