How hard is it to replace a laptop's thermal paste on your own? My laptop's fans are running on full throttle and it also randomly keeps shutting down. Thinking of buying some good quality thermal paste on Amazon and applying it myself.

Before you do any of that.... If you're running windows, check the event log for 'thermal events' or 'thermal shutdown'. Chances are your motherboard is damaged.

for me just blowing the laptop's fan with the blower side of the vaccum cleaner solved 90% of the problems. Unless your laptop is really old, the problems shouldn;t be with the thermal paste

blowing the laptop's fan with the blower side of the vaccum cleaner

won't recommend unless you've removed the bottom of the laptop. Chances are it'll push the dust in other regions where they may create trouble in future