To change the time and date you may need to remove the face from the case to access the crown. However, it is also accessible in the case.
To change the time simply pull the crown out to it's furthest setting (or one click for the faces without a date function) and twist the crown to set your time correctly.
To change the day/date pull the crown out one click. Turn the crown clockwise to change the date. Turn the crown anti-clockwise to change the day. (Don't be alarmed if a day shows in French, simply continue to turn the crown and it will reappear in English. All day/dates are shown in two languages).