Can i overclock g3258 on Gigabyte GA-H81M-S2PH

First Download the CPU stability testing software prime95 from here :
http://www.ocaholic.ch/modules/wfdownloads/singlefile.php?cid=101&lid=758
Download only version 26.6 of prime95 bc the earlier versions produces a lots of heat.
Don't overclock by any software because overclocking is not the thing that can be done by software. First set the XMP memory profile enabled to set your RAM correctly. Then Go in BIOS and find the CPU clock ratio, this is the multiplier setting. It starts at a multi of A (some no.)x 100(BCLK)(normal factory settings) to give you A Gigahertz. So up it .5 at a time and boot to os and test with P95 for stability and monitor your temps. Do this for approximately 20 minutes. If it passes raise the multi another .5 and try again. You'll get to a point where either P95 won't pass or your temp will gone so high. If the temps gone high you'll have to stop and work on cooling. If P95 fails then go to the Advanced voltage section in bios and add some volts to the CPU VCore . Stay in offset and just add a bit by tapping on the "+" key and test again.
If your temp goes really high them you have to stop and keep it to cooling. A step will arrive when your P95 never pass or temp immediately go high. Them you have to stop overclocking and you get your extreme speed of your processor. ....


This is the method, but for overclocking you need a good cpu Cooler, which cpu Cooler are you using?
 


SeaSonic ECO 600W PSU