It's c# and not vb.net but it should be straight-forward to read and convert.
string ds = "25.05.2016";
DateTime dt;
if (DateTime.TryParseExact(ds, "dd.MM.yyyy", System.Globalization.CultureInfo.CurrentCulture, System.Globalization.DateTimeStyles.None, out dt))
{
ds = dt.ToString("MM/dd/yyyy");
}
Note, however, that dates don't have a format so there is no such thing as a DateTime class with a certain format, dates only have a format when you convert them to a string.