for those who look for upgrading, i suggest upgrade to ssd first (at least as boot drive), do a fresh windows install, then ram.

replacement of thermal paste is a good idea if your cpu/gpu temperature are higher than 85c under loads. note that this might void the warranty if you do it yourself. it's better to ask the service center if they can help you out. mx-4 is fine, but you can try gc-extreme for better effects (get this from apes.my).

if you're not that picky, you can go for mainstream ssds like liteon ssd s900 or transcend ssd370. they are not the greatest but they are affordable, and they are much better than hdd in terms of speed. (go for at least 256gb, or more if you can afford it) if possible, keep the hdd for downloads and storage (using a hdd caddy to replace the odd slot)

for ram, just stick to stock ram settings. don't bother to go for performance laptop ram. (higher clock speeds or tighter timings do not help anything in a laptop tbh)