Times: Once. Assuming you know what to do diet wise: Both during refeeding post fast, and afterwards.
Start here if posible: Adopt a high plant food diet (Fuhrman's recomendations are a good starting point). When you are happy with that, after three months, have a look at your BP readings. If nothing has change revisit the diet.
If you are using any animal products, stop. Limit yourself to a low level of unrefined carbs approx 100g dry weight per day. Take a close look at food combining and never over eat.
I assume all the normal "don'ts", alcohol, refined foods etc are understood.
If you want to reduce your BP faster then fasting is an excellent way to do so. But do learn how to eat properly first. Your eating patterns determine long term success.