Proabably need to have it un-hidden then check the units to see if they have it set. Having it hidden means you wont be able to turn it on or off.
I don't remember there being a game option to do auto promote but if there is you will need o go into World Builder (Ctrl-W while playing) to try and turn it off. World Builder game options are bugged on smaller resolutions as the screen don't have scroll bars to get to all the options.