Sure, you can either upgrade the current fan, or you can enlarge the hole for a 120mm fan. So that depends on how good you are with a tools like a dremel or a jig saw to enlarge the hole. Newegg has a good assortment of fans, you can search and sort by customer rating which can also help you pick one that is quiet. If you can measure the size of the fan (in milimeters) we can help pick one for you.
The other thing to do is upgrade the thermal paste under the cpu, the factory stuff will be junk. Fresh paste like Arctic Silver 5 will let the cpu run 7-10C cooler. You can also upgrade the thermal past under the other heatsink which is the northbridge. You would of course do this with the power unplugged and you clean the old thermal paste with isopropyl alcohol and let it dry. New paste is applied by putting a small dab in the center, the pressure of the heatsink will squish it evenly.
I wouldn't worry about the PSU until it fails, I would suggest however to use a good surge protector like one from Tripp Lite they make units that clamp at 150V.