Turn off the device and unplug it

Remove the heatsink or cooler

Clean old thermal compound from the CPU/GPU and heatsink with isopropyl alcohol and a lint-free cloth

Let all surfaces dry completely

Apply a small pea-sized dot or thin line of thermal compound to the center of the chip

Do not spread it unless the compound manufacturer instructs you to do so

Reinstall the heatsink or cooler straight down

Tighten mounting screws evenly in a cross pattern

Do not overtighten

Check that the cooler is seated properly

Reconnect power and test temperatures