Hi,
you need to
1. log on to the back end
2. on the left hand side navigate in the menu to Events (or whatever it is in Frensh)
3. there click on Settings
4. on the top choose Display
5. on that page you find settings to change the display format for the dates and times
the direct link is: http://<yourpage>/wp-admin/edit.php?page=tribe-common&tab=display&post_type=tribe_events
Hope that helps
Tom