Hi,
For this please contact WPML support. They are the right people to help you out on this. Besides, here are few links that might help you.
http://wpml.org/forums/topic/language-switcher-flags-only-2/
http://wpml.org/forums/topic/how-to-adjust-flag-switcher-in-menu/
http://wpml.org/documentation/getting-started-guide/language-setup/custom-language-switcher/
Hope that helps. Thanks!