Removing The Original Thermal Paste
If the processor and/or cooler have thermal paste on them, you should remove it before applying a new thermal paste.
In Figure 8, there is a Sempron processor that was originally mounted with a cooler that already had thermal compound.
In this case, first you must clean off the remains of the thermal compound. Use a cotton swab with isopropyl alcohol (isopropanol). This kind of alcohol is purer (doesn’t contain water) and can be found at electronics equipment stores or drugstores.
You can also clean the rest of the thermal compound that remained on the heatsink. We used a utility knife to rub out the rest of the compound, being careful not to scratch the cooler base. To finish, use a piece of cloth with isopropyl alcohol (isopropanol) to remove the rest of the thermal compound.
With all the remains of the thermal compound removed, you can now apply the new thermal paste.