You cannot download a "v1.4 ROM" directly; instead, you must apply an update file to your base game. Obtain the Update : You need the v1.4 update in Install in Citra : Open Citra, go to File > Install CIA , and select your update file.
Warning: Do not use "Walk Through Walls" near the Mossdeep City space center, as it can break the 1.4 event flags. Pokemon Omega Ruby 1.4 Citra
How does Omega Ruby run on Citra?