Overclocking can be done on the Z170 Extreme 7+ in a couple of different ways. The easiest would be the OC Tweaker section of the A-Tuning software. This can all be done within Windows.
If you actually go into the BIOS there is a “Load Optimized CPU OC Setting” which will give you set overclocks depending on your processor.
Finally of course you can fine-tune things manually in the BIOS yourself. Using the same process we did with Haswell we were able to bring our Core i7-6700K up from 4.0 GHz to 4.7 GHz. This was achieved by simply setting the multiplier to 47 and changing our CPU core voltage to 1.35V. This is a 100% stable overclock as it passed all of our benchmark tests as well as a stress and temperature test.