Have you tried? Ive never had much sucess with overclocking, It depends what your motherboard will support. Remember cooling when your considering overclocking & i hope you undertstand your not covered by warrenty from the supplier if you overclock.
Some motherboards will be able u to un-lock the multiplier, I would definetly research before you do, there is many dedicated overclocking sites and forums i cannot remember them off the top of my head google is your best friend.