You are doing right when you change the voltage on the BIOS. Also, change to manual. Then if the voltage is too low to support your overclocking, the system will become unstable. At this point, raise the voltage slightly.
That's not the point, I know HOW to lower the voltage, I did it a little bit already, but when I try putting it lower than 1.4 (it is at 1.35 at the moment in the BIOS) it still runs at 1.4V.
I don't have any kind of power management turned on or anything like that.