Get in good physical shape, or exercise regularly. Eat the right foods (stop any junk). Lose weight if you have any extra pounds. Don't smoke. Decrease your sodium intake.
It is almost impossible to lower the diastolic pressure without lowering the systolic pressure also. The only difference is the contraction or stroke of the heart, right? In a healthy person, blood pressure is regulated by the expansion of the arteries, when the heart contracts, and the contraction of the arteries when the heart rest. The arteries act as accumulators, they either expand to limit the peak increase in BP, upon a beat, or contract to limit the peak decrease in BP, when the heart rests. Without this elasticity of our arteries, our BP would be something like 245/25. Our veins are totally different and do not have this property. Of course there are hormones and other components of our blood, that effect BP.
As we age, our arteries lose some of their elasticity, and is why most people's BP increases with age. Arteriosclerosis really effects this elasticity, and can be a natural result of aging, and can be accelerated by smoking and other bad habits.
Hope you don't have any bad habits and please tell everone what this confounded drink consist of, Ha ha aha