GTS 250 overclocking

For OC software I'd say MSI Afterburner. It's pretty good and easy to use. You'll probably want to look up GTS 250 OC guides/benchmarks to have an idea what other people are getting. Temps I'm not sure about that card in particular but generally under 80C is really fine... many cards can hit 100C and be ok but I don't think that high is safe on this card.

thnks man

I think your card is already overclocked!

no its not overclocked bcoz nvidia gives 738/1836/2200 and it is 680/1632/2000

738/1836 yes but the memory clock 1100 as Nvidia specified, not 2200 and that what really matters in GPU OC
Anyway for a simple way you can try (Gigabyte Gamer HUD Lite) util But I am not sure it is going to work on your card since it is from a different vendor.
otherwise you can try RivaTuner
http://www.guru3d.com/rivatuner/

thanx man