Assuming the monitor was setup correctly you should be able to change it by executing gnome-display-properties (either via a terminal or run application)
Not sure where you'd find it in through the menus in Ubuntu (maybe in the gnome control panel). I fear that this question may lead to how do I setup my monitor correctly because 60 is your only choice
Its System --> Prefrences --> Display.
And for the OP, if you need to change to the nVidia proprietary driver, look here
. Though thats probably going to be when and not if.