Download and install; once finished, the title screen will display "Ver 1.4".
If you are using a 3DS with Luma3DS or other custom firmware, follow these steps to install the update manually. pokemon omega ruby update 1.4 cia download
Because direct linking to copyrighted files is not possible here, you should look for the following reputable sources (search via Google or Reddit): Download and install; once finished, the title screen