Flags can be set up in the widget, not in Transposh settings
When you choose the widget you may change its style, this is not in the plugin options but in the specific widget appearance, in the same place you can change its title, etc.
So basically:
1: upgrade to TRansposh full version using the setting page
2: remove the old widget (Appearance>Widgets) from the sidebar
3: drag the widget to the sidebar
4: in the widget option select whatever you choose, e.g. Flags
Thanks.