Question About Religion

[Bex372]

I'm playing a game where I want to have an AI's religion become my own but I can't do it in diplomacy. What do I have to do to adopt his religion?

 

[dx8976]

you have to wait for his religion to spread to at least one of your cities.
open borders and trade routes are supposed to make it ha a better chance of happening.
you can switch religion at the religion advisor screen (?) by pressing F7.