go into your bios and look for xmp. It should look something like this:
http://media.bestofmicro.com/I/H/345401/original/asus_p8z77-v-lx_1.png
That's for an Asus motherboard but if your's isn't there should still be something similar
XMP is an auto setting to get what you paid for so you don't manually have to adjust the timings, voltages, etc. Your ram as paid for is rated to run at 1600MHz cas 9 at 1.5v so simply changing the default to the xmp profile should fix that for you.