Open the FBI application on your 3DS home screen.
Ensure the update CIA matches the region of your game (USA, EUR, or JPN). pokemon x update 15 cia link
If the installation fails at 99%, the download may be incomplete; try downloading the file again from a different mirror. Open the FBI application on your 3DS home screen
Once finished, the version number "1.5" should appear on the bottom screen when you launch the game. Safety and Legality the download may be incomplete