If you already have a Premium Subscription and you want to upgrade it, you have to:
1. Go to the "Store" tab.
2. Tap on "Courses".
3. Choose to which level you want to upgrade your Subscription and tap the "Subscribe" button.
Note: If you upgrade your Subscription, the new Subscription will begin instantly, canceling the old one. The price of the Subscription may vary according to your location.
How do I subscribe?
How do I manage my Subscription?