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#31
Here is a video showing how to clean a case. Two cautions, though.
One, if you have a fan on the side panel of your case, don't just yank the side panel and fan cable off like the guy in the video did. Tip the panel enough to see where the fan cable goes, then reach inside and carefully unplug it, noting where and how it is plugged in. That will avoid possible damage to the cable and the motherboard and will let you see where to plug the cable back in when you are done.
Two, there is good chance the CPU cooler fins are choked with dust. You may need to remove the fan on the cooler to do a good job of cleaning them out. Remove the fan only; do NOT remove the cooler. The cooler has a thermal paste between it and the CPU and, if you remove the cooler, the paste will need replacing to avoid destroying the CPU from overheating after you replace the cooler. It will be much easier for you to just to leave the cooler in place.
I suggest using a cotton cloth instead of paper towels. Paper towels will shred on sharp edges and will make more work for you to clean up. Wooden toothpicks are useful for dislodging dust from tight places, such as between the fins of the CPU cooler. They can also be poked through a grill to keep fans from spinning. A thin piece of cardboard, such as a business card, also works well between fins; just don't use plastic.
Again, do not disassemble your graphics card, including the fans for the same reason you do not want to remove your CPU cooler. It will be easier if you can remove the card (after removing the PSU cables, remove the two screws on the bracket on the left end and release the latch on the right end of the socket on the motherboard socket) but, if you have to force it to get it out, just leave it in place. Spray air between the fan blades (without spinning the fans) to blow out as much dust as possible in the heat sink fins. If using canned air and the card is still in the computer, bend the straw to keep the can upright to avoid spraying liquid which could damage components. A partially filled can is easier to use here. You can also spray air through openings in the sides of the card.
If the computer is really dirty, you can figure on spending an hour or more getting it clean again. It isn't difficult but it is tedious and time consuming (I have seen cases so filthy, it would take all day to clean). Once you get it clean (it doesn't have to be brand new clean, btw), the more often you clean it, the easier and faster it will be to clean. How often to clean it will depend on where you live. I live in a dusty desert. I vacuum off the outside of my case and dust filters once a week (do not use a vacuum on the inside!), then blow out the inside of the case and back blow the filters once a month. It takes me less than minute to vacuum the outside and ten minutes or less to blow out the case as long as I do it often enough.