I have the CM HAF 932. The three large 230mm fans are low speed fans but they move quite a bit of air due to their large size. You cannot increase the speed of those three fans.
Are those the fans you are referring to or are you referring to the exhaust fan on the rear panel or perhaps a cpu heatsink fan? What makes you think you computer is running hot? Did you run some sort of utility to measure cpu and core temperatures? What is your ambient room temperature?