I already upgraded to upgraded to JotForm Premium Bi-Yearly. Will my rates change with the increase this month?

Sorry about the confusion. That email was actually only intended for free users.

You will keep your existing low prices as long as you wish to keep you subscription. All existing subscriptions are grandfathered. The new prices only apply to new subscriptions. 

So, no, you don't have to do anything else to lock in the low prices. You already have them.

Can you clarify a little more about "subscriptions?"  If I am a free member and I pay to upgrade for $90 year, is that $90 year a "subscription" that will lock in or do I have to pay the $9.95 per month to lock in?

If you pay before the 15th you will be locked to the plan you have paid for at that rate i.e

for $90 year you will be locked in to $90 per year which is renewed yearly

for $9.95 a month you will be locked in to $9.95 per year which is renewed monthly