The national spirit in question is "iliterate_population". Apparently you cannot change it in game, since you cannot remove national spirits. What you can do is play with the files in common/national_focus folder and add to one of the focus tree entries a line within "completion_reward" parentheses:

remove_idea = iliterate_population

Of course depending on the level of the spirit you have (there are "iliterate_population", "iliterate_population_1" and "iliterate_population_2").

Thanks delete013 for the help