Summarize the following:
You don't have to clean the main air ducts, but you can do it if cleaning out as much dust as possible is your goal. First, check to see if you have rectangular duct work. If so, go ahead and slide the drives down with the use of pliers. Then, pull the caps off of the slips. The terminology may sound technical, but it should be pretty easy to figure out when you're standing in front of it. The drives are the long, vertical pieces of metal on your rectangular duct work. Take your vacuum hose and slide it into the space created by removing the caps. This should be pretty easy to do, unless the duct is up against the wall. Vacuum out as much dirt and dust as possible. Then, check out what you've done with a flashlight. Vacuum again if doesn't look as clean as you'd like it to be. This is only necessary if you actually have a basement. Usually the duct work in your house will have a few registers dedicated to the air flow in your basement. Take off those registers and vacuum inside of them. Hopefully the job has been done to your liking, but it's okay if you couldn't clean the ducts as well as you would have liked. Some problems, like mold, are too big to handle on your own. If so, call in a professional.
Take the caps off of the rectangular duct work. Vacuum out the dust. Remove the inside basement registers. Call in a professional.