1. Open the app.
2. You will see on the top part of your home screen a slider - swipe through the slider and find the "Go Prime" button. Or you can go the settings menu and tap the "Get unlimited scans' button. Tap on it.
3. You will have two options - "Unlimited" or "50 Scans Monthly". Choose the one you prefer and click "Get Prime Unlimited".
4. Fill out the details and once you're done, you will be a Prime user.
If your app doesn't update immediately and you still see a limitation of scans, please go to the settings menu and tap the 'Restore purchases' button. This should enable Prime and you should be able to enjoy all the Prime features.