First create a DateTime
object from your string
DateTime dt = DateTime.ParseExact("12/06/2014", "dd/MM/yyyy", CultureInfo.InvariantCulture);
Then from that object you can achieve anything you want like this
dt.ToString("MM/dd/yyyy");
OR
MyDateTimePicker.SelectedDate = dt;
EDIT: According to your requirement do this
MyDateTimePicker.SelectedDate = dt.ToString("yyyy-MM-dd");