Then you need to go into BIOS. If you don't know how to access BIOS then you need to press the "Delete" key during POST (before the Windows loading screen).
Once you're in the BIOS, go to the M.I.T. tab, then "Advanced Frequency Settings". Make your way down to "Extreme Memory Profile (X.M.P.)" and select a profile (there will be two profiles, one of them will be the 1600mhz profile but you will need to test this out yourself). Once you're done press F10 to save and exit.