Cpu voltage question?

i have a soyo dragon plus motherboard. i am running an amd athlon 2400+ processor. it runs stock at 2.0 ghz and i hve 1.5gigs of ram installed. although my bios does allow me to chagne my fsb, i am unable to overclock the cpu past 2.07 ghz speed without changing the voltage. my question is does any care to tell me how to change the voltage safely with the bios?