Tap Upgrade (some devices may display an offer in the icon).
Select one of the subscription options and tap the 30 Days Free button.
Tap Subscribe. Your purchase will be completed using your Google Play account. Follow the on-screen instructions to complete your purchase.
Type your Google Account password and tap Verify.
Tap Finish. When your purchase is successfully completed, your license will be updated automatically and you will have access to the premium features immediately.