Use a lint-free cloth to clean the old thermal compound.

If the thermal compound is solidified, you can use a flat end of any plastic tool to scrape it off.

Use again cloth with isopropyl alcohol to clean the Thermal surface.

The Fan and Headsink are held together with a large black bar. Removing the tape at both ends, to separate the Fan from the Headsink.

Use a soft anti static brush and clean the Heatsink on the inside.