use a paper towel, dampened with Rubbing alcohol. make sure you remove the processor from the motherboard first, and hold it/put it somewhere where the pins wont get bent. Also, if it is a processor that doesnt have in Integrated Heat Spreader (looks like this)<<IHS or THIS<processor withouth IHS. If it doesnt have an IHS, be EXTREMELY CAREFUL when cleaning it off, and applying thermal paste. and dont use a ton when you apply the new stuff. use a thin layer.