Operating system is not given, but this should be independent of OS:
Try entering the BIOS setup at system boot. Exactly how this is done depends on the manufacturer of your BIOS software (usually you press F1/F2/Delete/some other button during the very first screen that shows when you boot - which button is often indicated somewhere on this screen, or in the manual for your motherboard).
See if there exists a graphics setting for switching to "Dedicated graphics", "Discrete graphics" or something similarly named.
If so, enable this, save and exit.
This works on my Acer laptop. Not all motherboard manufacturers give the option to control this on a BIOS level, though, so you may be out of luck on this level if no such setting exists.
I point out once again that the motherboard manual should have more information on this.