You haven't mentioned your weight and that could be a factor. Exercise alone is not enough.
A blood pressure of 140/90 is borderline hypertensive and blood pressure is generally managed in steps. Step 1 is diet/exercise/change of lifestyle. Step 2 is adding an antihypertension medication to Step 1. Step 3 is adding a second medication.
Start with Step 1. Change your eating habits, continue your exercise and learn to effectively manage or avoid stress
and stressful situations. If you drink, stop or cut back. If you smoke, stop.
When these measures are ineffective or only partially effective, it's time to move to Step 2. Antihypertensives are safe, MUCH safer than having hypertension!