First, go to Settings->Backup and Restore->Backup Library on the old device to create a .msb file if you haven't already. Then go to Settings->About->Deauthenticate License on the old device so that you use the license key on the new device instead. Then restore your library using the .msb file that you generated. Also, just so you are aware - a license key can only be used on a single device at a time. You cannot use the same license key on two devices. For users that want to install the app on multiple devices with a single purchase (devices that they own and will be personally using), they should go through the Google Play Store.
Mike
Mike