Please list full system specs when asking such a question. Cooling is my primary concern here.
Other than that just follow one of the numerous overclocking guides available (like the one already suggested). Post up your results and we'll be happy to help if you get stuck or confused at some point.
i have a asrock 970 mb extreme3 with 12gigs of memory sli cards 570 ti's 975 be processer and a h60 watercooler cam i overclock and if so how i am new at this. win 7 64 bit