if you have "2014-12-25" in string variable you should parse it first and convert it to a DateTime
var dt = DateTime.ParseExact(FromDate, "yyyy-MM-dd", CultureInfo.InvariantCulture);
Console.WriteLine(dt.ToString("MMMM dd, yyyy"));
but if you have "2014-12-25" already in a DateTime
variable it is just a matter of formatting. just use
Console.WriteLine(FromDate.ToString("MMMM dd, yyyy"));
list of date time formats