Basically you would have to enter BIOS and set everything for the memory manually. You will though not see any noticeable performance increase.
Thx for your answer but i know i need to set manually and here is the problem i dont know how. So if anyone know how to do that will be nice to post here.
P.S. for the difference between 1600 - 1866 i know is not big but still if i have memory on 1866 i would like to be able to run at that speed.