Please log out from the app and log back in - you should have a premium account with all features enabled.
Make sure to use the premium account credentials (username OR email address and password).
Note that username IS case sensitive.
If logging out and in does not help and the purchase has been made via iTunes or Google Play store please try to "kill" the app and open it again OR reboot the phone.
The HOME --> Missions screen will look like this after the upgrade (the 'upgrade' button will turn grey):