Your existing Premium subscription will automatically carry over to Public Reserve. Your price will be protected for a period depending on your billing cycle:
Monthly subscribers: Your price stays at $10/month for 12 months. After that, it renews at $20/month.
Annual subscribers: Your price stays at $96/year for one more renewal cycle. After that, it renews at $200/year.
You don't need to do anything, and the transition happens automatically.