It might depend on your carrier version, but on T-Mobile's is in the messaging app, settings, Chat settings (turn off 'send read receipt' and 'share typing indications'). There used to be a way to turn RCS off completely on Samsung phones, but it seems, at least on the T-Mobile version (on the Sprint model I believe it's under Enhanced Messaging), that the only way to turn it completely off is to turn off 'Voice over LTE'.