In order to clean a cooler/cpu of previous thermal compound you need to use a high level of isopropyl alcohol fluid. I use 91%, the higher the better. Be sure to dampen a lint free cloth with the alcohol, I use quality coffee filters, and clean off both surfaces. Make sure that (they) are 100% clean. The amount of thermal compound you want to apply varies on the CPU, you probably only need a tiny dab in the center about the size of half of an uncooked grain of rice. I use artic silver 5, I have tried several other brands and I feel over all this one is the best. The higher the silver content the better. Why silver? Do some research on thermal conductivity. I am worried you might mess this up concerning
(considering) you are asking this question. If you aren't certain about doing this, I would seek in person
(someone's) help.