Overclock means test-fail, so, you need start to "play" with the setting in your BIOS.
Some tips before you start: Look for the max temp of your CPU and max voltage, check in Google the result that other peoples has with the same CPU that you have, you will not be able to use the same settings since all the specifications are different but can give you an idea how start and the limit.
If you need more help, let me know the specs of your rig.
CPU frequency = CPU multiplier x FSB. In my case my CPU is x16 (multiplier) x 200 (FSB) = 3200MHz (stock speed). My CPU has unlock multiplier, that means that I can overclock the CPU in three ways:
a- Rising the CPU multiplier, this not affect the RAM speed in any way.
b- Rising the FSB, this affect the RAM speed because both FSB and RAM speed are linked
c- Rising both CPU multiplier and FSB, this affect too the RAM speed.
Now your CPU has lock which means that you only can overclock the CPU using the FSB. Like I say up, when you change the FSB the RAM speed also change, so, slow down the RAM speed before rise the FSB.
How do you slow down the ram speed? In the BIOS you need look for "DRAM Frequency".