Hi vike,
The most cheap way to do this would be too add some case bracket fans they normally come together on 1 power lead. The best way to fit them is 1 at the back of the case and 1 should clip in the front of the case then this way you have 2 fans blowing from both sides on your Board, I just did this yesterday with mine and reduced my temperature from 55Oc to 35Oc.
But the best way to do it is to position one fan so it blows air out, and one fan so it blows air in, this way you have the Cool air blowing on the CPU and the other fan is blowing the hot air out, but before you do this make sure theres no cables in the way and you have a good all round ventilated case even possibly try and remove some PCI cards you may not need.
I hope this helps you