How do I clean dirt from mac fan is loud

I would recommend you down load a good thermal monitoring app like TG Pro. You’ll likely need to post an email to them to get the older version that works with your older OS-X your system is running. That way you can see which fan needs service.

You likely need to do some deep dusting out of your system. Get a small soft paint brush and a can of can’ed air and follow this guide to get the display off iMac Intel 20" EMC 2133 and 2210 Bildschirm austauschen carefully scrub the dust build up and blowout the dust with short blast of the can’ed air.