Download MSI Afterburner and Unigine heaven.
Start with the base clock and increase it a bit as well as the power limit, run Unigine heaven benchmark.
If it passes repeat all steps until you start seeing some instabilities (artifacting, crashes, ect.) or run into thermal limits.
Then do the same with memory clock.
If you feel confident you can unlock voltage control to overclock further.
I built my pc last month and I learnt how to overclock pretty quickly. It's not that hard once you get used to it.
Also if you need a more in depth tutorial refer to this guide: http://www.maximumpc.com/how-overclock-your-graphics-card-2015/#page-2
This is where I learned most of my info from.