If the object is to grow the largest possible pumpkin, then the main thing to do is to have as large and vigorous a plant as possible without any more fruit being set. You may need to pinch out side growth to keep the plant in limits and for light to get to it, but simply remove any flowers and fruit after the first two. I guess two are suggested so you have one in reserve if the other fails, but in principle for the largest you would just nurture one.
If you just want a big crop for eating, then allow many more smaller pumpkins to form, stopping new fruit forming once there won't be enough time for them to ripen on the plant. (depending how sunny your site is and how long the season lasts)
Rather like with a melon, you can allow the leader or main shoot to reach its desired length, and then by pinching it out, you encourage sideshoots on which more fruit will be formed.

thanks for that bertiefox will try it