do you have sufficient cooling. the stock cooler wont cut it past a 5 percent oc. which will be pretty much what your motherboard will do as its asus.
if you have the cooling then its a simple case of going into bios and bumping the ht/cpu bus multi from 200-207 or there abouts..(without a volt increase. this will be x'ed by the NB multi to give you your end clock. so you get 207x15 gives 3.1ghz roughly.
but really you need an oc guide... http://www.tomshardware.com/reviews/phenom-overclock-athlon,2161.html
this will give a better idea of whats going on and what your wanting to do.