fantasytears The late reply isn't an issue. I'm always around.
The high temperatures are likely the cause of the lag, since your CPU will throttle its workload to protect itself from heat damage. That means a major hit to performance for whatever is running at the time.
Since you're already elevating the laptop and it hasn't helped, it's possible that one of the fans is obstructed or a vent is blocked. If you're comfortable doing so, take the bottom chassis off and have a look. Move the fans manually (but don't spin them excessively) to make sure they rotate easily, and use compressed air to blow away any accumulated dust.
I believe you have a Legion Y540, and this video shows how to open the case. It's a RAM upgrade tutorial, which doesn't apply to you, so just watch starting at about 1:30 in until the chassis is open:
https://www.youtube.com/watch?v=nLmfHq-5R4M
If you're not comfortable opening the case, you can at least shine a flashlight on the vents to see whether you spot any blockage. Compressed air could help clear it, although without opening the chassis, you're mostly going to move around the dust rather than get rid of it.
Your laptop isn't old enough that I would expect the thermal paste to have completely dried out by now, but it is a possibility. So if the above doesn't help, you might want to take the system to a computer repair shop to get it repasted. A reputable shop should be willing to take a look for free or cheap, and repasting shouldn't be too expensive either. Call around and ask for quotes so you don't get ripped off.
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