You're not going to until you read the memory instructions.
That 1600 speed is an OC, check the packaging. That said you need to pull your BIOS up, unless you are running a pre-built computer read the last lines on the first few screens when you power-up your computer from a FULL shutdown. From here check through the menus for the memory/over clocking page, then follow your RAM's instructions for the proper settings.
Don't be afraid of your BIOS, You must confirm your changes at the end, so making an accidental mistake is incredibly hard. Just keep your fingers off the 'y ' key.