GPU

CPU

Take the ArctiClean #1 labeled as Thermal Material Remover and a clean microfiber cloth.

Put drops of the liquid #1 on the CPU's metal surface until it will be covered entirely and then wait 60 seconds. In the meanwhile look out for any leakage that may reach the motherboard and stop it. Once the minute has passed, clean the CPU with the microfiber cloth. Repeat the whole operation until you don't see any gray stain on the cloth.

Repeat the same cleaning operation described above on the GPU too.