its not hard to Overclock a GPU, but don't expect major performance boost its usually about 10-15% if your lucky.
Download MSI Afterburner and heaven/Valley benchmark run the benchmark and leave it running open up MSI after burner..
set up Power limit to max then start increasing the Core clock and Memory clock start off by 50 on core and 80 on mem and take a good look at the benchmark if its smooth/ no stutter, crashing or artifacts popping, then start increasing the ore by 10 and mem by 20 and keep looking for artifacts and let it run for a bit and make sure it does not crash then keep adding untill it either crash or artifacts start popping up. if you hit your gpu limit and still have acceptable temps then you can consider adding a...