How to clean fans and aply a new thermal paste?

Ideally, you'd want to use either a can of compressed air or a small dust blower to blow dust off the fan. For replacing the thermal paste you'll need to remove the heatsink from the CPU and clean any thermal paste from the heatsink and the cpu. You'll need an alcohol based wipe to remove the paste from both surfaces. For replacing the thermal paste you're just going to need enough to cover the surface, and not too much to where it is spilling over the sides of the CPU.