@CaioDA Just disable them from the admin control panel. Options > Disable then Save.
Is it really that simple? Now I'm embarrassed... But, going along with what @planner said and @psychobunny pointed out, this is a very developer centered forum software with an initially steep learning curve. It's not quite plug and play. I recommend something like Foundation's Joyride to introduce new users to the system.
Update: But currently, there is no way to remove them completely (unless a forum restart is required or override them). That's a feature I'd love to see.
@Rusdy-MT It seems to me like they have revamped this option. It's now some kind of "group privilege" now. You can toggle it under ACP -> Manage -> Privileges. This came out of nowhere for me as well...