That is a short question but actually answer is long. Basically we can say, you have to flip your heart for that, and change your arteries. Actually you have to flip everything that is in your body. And dont worry, it cant happen. But you can slow the speed of your blood going from arteries. Example: Doing a hand stand long time.
Your cells wouldn't get the oxygen they need, the fingers and toes would go first, then the arms and legs, your body would try to keep the blood going to the most important areas for as long as possible.