I haven't dusted my laptop in 2 years now (my apartment s very dusty)and the temps on the cpu are hitting 93 degrees so I think its time. I want to lower the temps more by changing the thermal paste too. I keep hearing people saying that the MX 4 thermal paste is great but it has 8.5W/mk while I found one from thermal grizzly that has 11.8W/mk. Will that make a big difference because they are quite similar in price(they're both dirt cheap)? Also is 4 gramms enough for my whole laptop or do I need 8 gramms?
The difference between thermal pastes is usually only a few degrees, I wouldn't worry about it too much. MX-4 is good, 4 grams is more than enough for one application.
Depending on your laptop model, repasting the CPU may require basically taking the entire thing apart. I would start with just giving it a good cleaning/dusting and seeing how far that gets you. I had the same dilemma only a week ago when I was trying to fix my gf's overheating laptop. I originally planned on repasting, but on seeing how much work that would have been I settled on just dusting it. Made a huge difference in temps (close to 20C I believe), and fans are now typically audibly slower than they used to be.