for starters, the fan is designed to blow onto the fins of the heat sink. It is direct current, so reversing the wires will reverse the fan blades, but they at designed to blow in one direction, and will not move air very well in the opposite direction. Kinda like a helicopter, just static air.
My suggestion is a duct mod to move the fan off the heat sink a bit. This increases airflow due to the fan motor itself taking up so much surface area on the heat sink.
Next freebie thing would be to look at intake of ambient air from outside the case. Most cases do not have adequate ventilation, as it would also promote dust accumulation, if not properly filtered.
Run if with the side panel off, see if the temps drop considerably. If so, start poking some intake holes in that case somewhere.