The first thing you need to do is to control your breathe. Breathe steadily, deep and slow. It really helps to relax your body and release the excitement and tensions within it. Secondly, take the entire process very easily and do not go around just penetrating your partner with a few hard thrusts before ending up. You should go nice and slowly, and understand that it is about pleasure and not releasing your frustration. Thirdly, you may consider masturbating before you have the real thing. Your second orgasm will take much more time as compared to the first one, which would definitely help you last longer with your partner. Fourthly, a great trick to stop orgasm is to indulge in some romantic communication with your partner. For example, you may tell her how great she is, and how you are really enjoying it with her. It also helps to develop a better understanding, and she may also give her feedback which is likely to further encourage you.
It is hoped that these techniques would answer the question of how to stop orgasm.