There are a few ways to overlock the Fatal1ty Z97 Killer. The easiest way would be to use the F-Stream software. Just navigate over to the OC Tweaker page in the software and change the values right there. All changes here are made in real-time so no restarting your system is necessary.
Of course you can do the exact same thing in the BIOS as well under the OC Tweaker tab.
Overclocking the Core i7-4790K is simple enough. On this motherboard I was able to get a stable overclock from its stock 4.0 GHz up to 4.5 GHz with a vCore voltage of 1.36v.