How to overclock a E7500 cpu?

I have a e7500 cpu. and my motherboard lets me overclock the cpu under my bios setting. I have messed all around like some people tell me and i can not get it to read over 3.9. I want above a 4.0. What do i have to do to my voltages to make it Go higher. I am afraid to make my core voltage to high and my fsb is up all the way. and nothing is different. I have NVIDIA and cpu-z, and hot cpu tester software all still tell me that its running at a 3.9333. I would like it higher. Please help