I have a question about a brand new Phenom II X4 995 processor(10 points best answer)?

I brought a brand new Phenom X4995 processor. I want to put it in my motherboard but since the heat sink already come with thermal paste. I want to use my AS5 thermal paste on the processor. Should I clean the heat sink first or I don't need to since is brand new? Will having two kind of thermal paste mess up my processor? I am noob to building computer.