I received an email that prices are going up on Aug. 15, 2015. I want to be sure I am locked in at today's price.

I received an email that prices are going up on Aug. 15, 2015.  I want to be sure I am locked in at today's price.  I currently have the Premium membership which I want to make sure I keep at today's price.  Do I need to do anything or will I continue rate unchanged?

Sorry about that. That email was actually only intended for free users. You will keep your existing low prices as long as you are a subscriber. 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.