There is a specific order you must follow when installing the game and its update.
This guide is for educational purposes only. Downloading copyrighted games (CIA files) that you do not own is piracy, which is illegal in many jurisdictions. This guide does not endorse piracy. pokemon x update 15 3ds world cia region f
If the “World” CIA still does not apply to your base game (rare, but possible with some Korean or Chinese iQue 3DS units), you may need to manually enable region-free mode: There is a specific order you must follow