If you purchased your Premium subscription through the App Store/iTunes and would like to turn off the auto-renewal, please follow these steps:
1. From the App Store, click "Featured" at the bottom of the screen
2. Scroll to the bottom of the page
3. Sign in with the same Apple ID associated with your purchase
4. Click "View Apple ID"
5. Enter your password and click OK
6. From Account Settings, click "Manage App Subscriptions"
7. Click on Cancel Hotspot Shield subscription