In my experience this behavior is caused by cooling fan(s) being clogged with dust/lint. This will require disassembly and removal of the lint.
You can probably find a YouTube video for your specific laptop model that shows you how to open it up. Keep track of the screws! Whenever I open up a laptop, I lay the screws out on the table in the same pattern (in miniature) in which they go on the laptop itself; that way, I keep track of which screw goes where when it come time to put it back together. This can be important because, for some laptop models, the screws are different lengths in different places.
You also might want to pick up some canned air to blow out any remaining dust from the metal cooling fins themselves. And if you have to take off the cooling assembly, which is a very thick piece of flattened metal wire attached to the center of the motherboard by 4 special screws and running to the cooling fan at the edge, you’ll want some thermal paste (also called thermal grease) to put back on the flat part when you put it back together (there may also be two flat parts). Not too much; just a very thin layer on the square area, and scrape off the old stuff first. If you have a Fry’s around they should have it; otherwise Amazon.
Here’s one I did showing before/after.