Every fan features a cubic feet per minute (CFM) rating, which measures of the volume of air it moves in a minute. The greater the CFM, the more air a fan moves. To properly air cool your computer, you need have enough case fans to push or pull air into and out of the case. More case fans means higher total CFM and more air being moved through your computer.
Just be mindful of the noise levels as fans can generate quite a buzz. To avoid making your computer too loud, use fewer or quieter fans. Also, flashing multi-color lights shouldn’t be the main feature of your case fans.