Don't even bother, if you need more performance, buy a better graphics card. The GT 610 is so weak that any overclock you do get isn't going to make any real difference. If you really want to try overclocking it, bump up your core clock by small increments, and test it out, make sure it doesn't artifact or crash. Once it does start artifacting, dial it back a bit and test again, that will be the limit of what you can achieve, since Nvidia cards have a locked voltage. Keep an eye on your temperatures while doing this, if it's getting really hot, eg. above 80 degrees, you'll have to dial it back, or see about setting a more aggressive fan profile if this card isn't passively cooled.