This was made to try and help someone that is new to working on a desktop. Is your fan too loud? Computer getting to hot? Those might be some reasons on why you should change your fan.
Step 1: Supplies
All you're going to need for this is a flathead screw driver and possible some zip ties.
Step 2: Unplug Everything
I personally think it is easier if you unplug all the wires from the back and move to an open area. If this is hard to do you will be fine just by disconnecting the power supply.
Step 3: Open the Case
Look on the sides of your case for any screws to be removed. I have thumb screws on the front and back of mine.
Step 4: Find Your Fan
Find the fan that you will be replacing.
Step 5: Follow the Wire
Follow the power cable that is attached until you see how its plugged into the power supply and unplug it.
Step 6: Unscrew the Fan
In my case the screws are on the outside but if you're using this to change more interior fans they will probably be inside right next to it. It helps to push the fan towards the back so that the screw driver doesn't move it around.
Step 7: Put Your New Fan In
Grab your new fan. Make sure the blades are pointing the right way. You should always have your front fan facing in to bring in cold air and your back fan facing out so that the hot air goes out. Some fans have arrows to show which way they're facing but if not you can tell by which way the slop is facing. If its going towards you then the fans is facing out.
Step 8: Optional: Wire Management
If you want you can use zip ties to keep your wires together so that its not a mess that next time you open it up. It makes everything easier and sometimes can even cool your computer by a degree or two.
Step 9: Put Everything Back
Just do the reverse of everything now. Screw in the new fan, plug in the power, and put the case back on.
Step 10: Optional: Computer Bios
Start your computer's bios and adjust the settings of your fan. Here you can set the strength of your fan, what degree you computer will get for your fan to turn on, and several other things.