Would you recommend taking my stock cooler out and replace it with a new fan? Or should I just get 2 more ( one being the exaust fan) fans installed alongside the already installed stock fan..?
You can do it piece by piece if you want.
You don't have an overclocking processor.
Is your ambient (room) temperature unusually high? Say above 27 C or 80 F?
The stock Intel cooler is fine for a non-overclock situation if you don't mind the noise it makes when it spins up above 2000 rpm.
I would NOT replace the fan on the stock Intel cooler. I'd either keep the Intel cooler as is or possibly replace it entirely later.
I'd probably just get one good exhaust fan and see if that did the trick Keep an eye on the temps in HWMonitor. Scythe and Noctua are 2 good brands to look for. If one exhaust fan doesn't solve your problem, then re-evaluate and maybe consider another CPU cooler. Be sure to get the right diameter fan and be sure to mount it so that it sucks air out rather than blows air in.
The most important thing is to get some airflow going from front to back. You don't have that now because you don't have anything pulling air out the back of the case.