Grip the heat sink by its copper pipes and remove it.

Don't grip the sharp, metal fins on the heat sink.

During reassembly:

Before removing any of the old thermal paste, note the location and quantity of thermal paste on the metal shield. This way you'll know how much to use when replacing it.

Use the flat end of a spudger to scrape up and remove as much of the old thermal paste as possible.

Remove all the remaining thermal paste and its residue with high‑concentration (>90%) isopropyl alcohol and a microfiber cloth.

Apply new thermal paste where the old paste was.

Firmly push the heat sink into place.