Karen has mentioned some excellent points here already. Another important consideration when trying to lower blood pressure is aquatic exercise. A study published in the Washington Post this July (http://www.washingtonpost.com/national/health-science/consumer-reports-w…) showed that exercising in water has great benefits for those that suffer from high blood pressure. Swimming lowered the blood pressure of study participants by an average of 9 points. This study was based on traditional swimming, although I’ve read other studies showing that exercises where you remain vertical in the water (as you might in an ‘aqua aerobics’ class) have the same benefits as traditional swimming.
Exercising in water produces similar aerobic benefits to exercises on land but does not raise the blood pressure as much during the exercise itself. This is because bouyancy applies less pressure to the blood vessels than gravity. It also means your heart doesn’t have to work as hard in the water; your heartrate may be 10-20 beats per minute lower in the water than it would be doing a similar activity on land.
One disadvantage to aquatic training is that it does not always lower adiposisity (body fat), which can also contribute to high blood pressure. It’s for this reason I’d recommend exercising as you’re comfortable (as long as your doctor says it’s safe for you) both in water and on land so you can reap the benefits of both. If you’re not used to exercising regularly, start slowly- maybe just a couple of days a week for half an hour or so. Remember that anything is better than nothing! If you’re not comfortable in the water, most pools have belts available. You can use them to water jog or to give you some confidence with swimming.
Here’s another article I think you’ll find to be helpful: http://www.mayoclinic.com/health/high-blood-pressure/HI00024
Best of luck to you in your fitness journey!