If you purchased a monthly plan before September 16, 2015, your account was upgraded automatically. If you're currently on an annual plan, you'll continue to renew annually at that rate. If you select a new monthly plan, your annual plan won't be available to you.
I missed this last night, but Apple has rolled out the updated iCloud pricing scheme they announced last week. My account was automatically upgraded to the 200GB/€2.99 plan, which I'm primarily using for storing photos and videos. I'm going to keep paying for iCloud storage, but I wish I could use it more.