How to remove the heatsink fan on asus cm5570

I was wondering how to I remove the heat sink fan on a Asus CM 5570 Desktop computer. The fan is making a noise after being turned on for about 20 minutes. I did take the side cover off and cleaned the inside of the computer out and cleaned the fan the best that I could, but this only lasted for about 20 minutes and then it starts making the noise again. Can you tell me how to remove to the fan and replace it.

Thanks, Kim