First of all there are some risks if done incorrectly but most cards have protection from that nowdays anyway.
You want to install an overclocking program I personally use MSI afterburner and also some kind of GPU stress tester.
GPU Stress tests:
http://www.ozone3d.net/benchmarks/fur/
https://unigine.com/products/benchmarks/valley/
MSI Afterburner:
http://download.msi.com/uti_exe/vga/MSIAfterburnerSetup.zip
In the software you should see three sliders that you'll be using such as: 'Power Limit(%)','Memory Clock(MHz)' and 'Core clock(MHz)'. Firstly without doing anything run the stress test and take note of the temperatures and frames. Then on the software increase the 'Core Clock' by 20 and press 'Apply' but after every time you...