How do I update the firmware on my Xbox controller?

How do a firmware update on my Xbox controller on iPad. for about two years now I’ve been waiting to figure out how to to do this, my brother hooked it up to a Xbox, and he said that it was updated, but it turned out not today. It always says “make sure your Xbox controller is turned on in range” or something like that. I’m very keen on updating this controller to play Minecraft with my friends thank you