Homebuilt,or store bought? If store bought may be out of luck
Download CPUID Hardware monitor (good for looking at voltages). Download CPU-Z
Simply google it. Look at memory tab and it will show you what you are presently running at. Then look at the SPD tab, it should show what speed/CL settings and at what voltage.
Look at the manual (if you do not have, download from Manuf.) for how to set CL values (hpefully you can). EX. for My gigabyte MB I go into Bios, goto M.I.T and hit Cntr F1 to get to settings.