Removal of the current heatsink involves depressing the sides of the mounting pins from the back of the board with pliers(don't scratch the board).A gentle push out from the back once they are closed with pliers should be all it takes. Sometimes you will have to very gently twist the heatsink back and forth to loosen the thermal paste that was on it after the pins are pushed out of the board(take your time it will release). Take sure you have thermal paste if you go this route, you will have to apply new stuff after taking the heatsink off.
The only issue with a fan swap is that the fan it self has the airflow that heatsink was designed to work with. As such a quieter fan may not push enough air to keep it happy(cool).
You can try it, but will have to keep an eye on chipset temps. just remember 60c does not hurt chipsets some run even hotter. Just log a before and after when running 3dmarks or something.
If you have room, you may be able to remove the current fan and mount another one(larger and quieter) over the chipset and cpu. Zalman has a bracket(BR123) that can hold a fan over those areas. I have had good luck with that idea in the past to cool a cpu.
Only issue is that bracket may be too thick to fit your case(I can not confirm[fit or not] this without the case here). I am sure something similar can be made with strapping from the hardware store. The included 92mm fan is NOT quiet unless it is under volted, just a warning.
I would just try with the stock fan and go from there, if its too loud.
-Replace it
-Try to lower its speed and keep an eye on temps.
-Blow(well suck) hole cut into the top of the case?(are you a modder?)
EDIT, do i see a spot for a fan up top? you may be able to mount a low speed 120mm there to cool the chipset and cpu
You would have to drill some holes for the screws, but it may be an option as well