When you say you can't change the modes, do you mean you can't edit them or can't change the screenmode?
If you want to change the screenmode select the system settings from the drop down menus, then select screens. Once you've go that, double click on where it says Ambient with the name of your gfx card. That'll bring up the "edit screen" window where you can choose a skin and the resolution for the Ambient screen.