Ugh, I need to do that to mine, and I have never done anything like that. But mine has gotten very loud, and I'm sure I'll find all kinds of crap inside it. I'm just a little scared about having to put the fucker back together again.

There will be a huge number of different size screws to keep track off, but it was actually easier than I thought it would be.

I looked up instructions on line for my specific model and that was a huge help.

 
 

Also the microsoft free thermal analysis tool  helps find out exactly how hot its getting.
Google it and choose a download site you prefer.

SpeedFan ...

Yeah SpeedFan is ok, but tempts you with too may options. If you just want a quick check then TAT or Mobmeter are good free choices.
All of these programs show slightly different temps but are pretty close. Actually if you do a reboot and go straight into bios there is often a section there that shows temps. Most laptops will shut down with a warning if they go over 100c. Mine was getting really close.

This laptop overheats occasionally, and it's clean inside and out ...
I've used SpeedFan on AUTO for a few months now with no issues ...

One thing you should think about is if your machine is clean and still overheats is the thermal bond between the heat sink and processor.
It could be that at some point it was cleaned and the surfaces on the heat sink / processor weren't cleaned and properly reseated.

I've seen that thermal paste get hard and flaky and if it wasn't properly removed and replaced then that could be a reason it would show high temps even when clean. 

Yeah, I thought of that, however, I don't want to rip it apart at this time ...