If it's this one, I have the same as a HTPC(lol).
This thing comes with a preinstalled 120mm silent-fan in the front.
There are also provisions for a rear fan, plus 2x80-120mm sidefans, although they are not included.
I suggest:
-Move front fan to the rear, suck.
-Install new highflow 120mm fan in the front, push.(I prefer LED, so you can see from far if the pc is powered on or not)
Test.
If it's still bad, install the additional sidefans.
Rem: Where does cpu cooler push the air to? Not to the top i hope?