How to make it *stop* overheating?

Well, I have a laptop. And there's a problem with it. It overheats often. I checked; it overheats every hour, and because of that, it shuts down more than once, every day. I want to make it stop. I thought there was a virus. And I use Advanced System Care, for 'cleaning' the files on my laptop which are unnecessary and possibly bad, but while it makes my laptop work faster, it doesn't help against overheating.
A few years ago, I could use my laptop all day long (actually, 12 hours was the most I was ever on in 1 day) and it didn't overheat. But now, I can't even use it for 2 hours without overheating and shutting down! Anyone help?
And, no, I can't get myself a new laptop. At least until I go to high school (here, you start high school when you are about 14 or 15) or college (which is only because my screen broke and I have an extra screen, but now I can't take my laptop with me because then I would have to take the extra screen as well and I can't imagine how to do it without breaking the extra screen, so my parents would get me a new laptop then.)... Please, help!

I found the older my laptop got, the faster it heated too. It might be as simple as needing to clean the fan or using a laptable (pillow with a table on one side of it. I have one for drawing, its handy) or something so the bottom of the laptop can breathe. Otherwise if those don't work, see if a techy can open it and clean out the inside. Usually mine goes back to normal after being 'dusted' like that.

And how do you clean the fan?