Once installed, you should see "Ver. 1.5" or a small "Update" badge on the Pokémon X icon within the Citra menu. Conclusion
This update is mandatory for all online functions, including Random Matchups, Online Competitions, and the Player Search System (PSS).
It looks like you’re looking for —likely for emulation (Citra) or a modded 3DS.
files for updates, emulators often require these to be decrypted first. How to Install in Citra: Open Citra. Navigate to