Getting a new case would be a good idea.. You've not mentioned your budget so i'll be assuming it to be moderate for now.. In case you don't mind a bit noisy environment in favor of great cooling then check out the ANTEC 900 2 ... Its a complete package that'll do any gamer proud ( personal opinion ).. For a raised budget, you can give the cooler master HAF series a look ( they are excellent but i personally found them to be ugly.. 932 is more uglier than the 922 ).. Finally at the pinnacle you can go for the ANTEC 1200 or the cooler master sniper..
Well, if your existing temperatures are balanced and fine then there is no need to improve airflow. I recommend first getting data on the temperatures of different components of your computer first and posting them on the website for us to see.
My recommended software to you is CPUID Hardware Monitor. Its free, light, and very good at getting temperatures from the computer. Post temperatures of your CPU, GPU, HDD, and MOBO if possible. Then if temperatures are to high, we'll further discuss what to do to improve airflow. You should also tell me your existing computer case and very detailed hardware specifications of your computer. That way we'll know which temperature ranges are the best for your specific hardware.
Try to locate your case where the air come and go well like beside window.Make sure that your case has enough distance from back side and if you use stand CPU fan make sure the airflow is in the right way (from front to the back).you can easly speed up the GPU fan with Cata or Riva.If it doesnt work go for extra fan or new case.