If you purchased the Advanced Feature Set (AFS) from inside the app, it should install automatically. You should see a message saying it has been installed flash across the screen.
If you purchased at our website, you can open the PocketBible app on your device and choose Buy/Apply Upgrade from the menu (tap on the PocketBible "dove" icon in the upper left corner of screen to reveal the menu).
An easy way to tell if you have the AFS enabled is to look in the action menu at the top of the screen for the Listen option. If it appears, then the AFS is enabled.