Depends entirely on the laptop.
My Asus was a PITA to take apart - had to disassemble the whole thing, literally because the heatsinks were on the keyboard side of the motherboard.
My MSI... take off the bottom access panel using 5 screws, and then another 5 screws for the CPU/GPU heatsinks.
My friend's VAIO..similar to my MSI, except the entire bottom plate comes off instead of just an access panel.
That's why I like my MSI - I can turn on the 100% fan boost whenever I want
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