Select "Elmedia Player" --> "About Elmedia Player" option from the main menu. If you are using the PRO version, you will see your registration name and the license type specified in the "About" screen. 
Additionally, if you have the PRO version, "Activate PRO version" menu option is changed to "Change License Type".
Purchase PRO Version
"Purchase PRO Version" menu option is always available, no matter what Elmedia Player version you have (free or PRO). It is needed in case you decide to change the license type you own (for example, Personal License to Company License). To see all license types available for Elmedia Player, visit https://www.electronic.us/products/elmedia/purchase/.
In the PRO version of Elmedia Player, all PRO version features become available.
Checking PRO status on Mac App Store Versions
The Mac App Store hosts 2 versions of Elmedia Player - Elmedia Video Player and Elmedia Universal Video Player. To check if you have PRO in Elmedia Video Player, go to Elmedia Video Player - About Elmedia Video Player. If your player is upgraded, the name of the app will show up as Elmedia Video Player PRO. 
On the other hand, the Universal Video Player already comes with unlocked PRO features. It doesn’t need to be upgraded. For more details about their differences, follow this link.