As I don't know the string format and the format I want to get, I created a function:
Friend Function FormattedDate(ByVal sDate As String, ByVal sFormat As String) As String
' Funçao para formatar a string contendo uma data em um dos 20 formatos abaixo no formato desejado
Try
Dim sDates(19) As String
sDatas(0) = "dd/MM/yyyy"
sDatas(1) = "MM/dd/yyyy"
sDatas(2) = "yyyy/MM/dd"
sDatas(3) = "ddMMyyyy"
sDatas(4) = "MMddyyyy"
sDatas(5) = "yyyyMMdd"
sDatas(6) = "dd-MM-yyyy"
sDatas(7) = "MM-dd-yyyy"
sDatas(8) = "yyyy-MM-dd"
sDatas(9) = "dddd, dd MMMM yyyy"
sDatas(10) = "dd/MM/yy"
sDatas(11) = "MM/dd/yy"
sDatas(12) = "yy/MM/dd"
sDatas(13) = "ddMMyy"
sDatas(14) = "MMddyy"
sDatas(15) = "yyMMdd"
sDatas(16) = "dd-MM-yy"
sDatas(17) = "MM-dd-yy"
sDatas(18) = "yy-MM-dd"
sDatas(19) = "dddd, dd MMMM yy"
Return Date.ParseExact(sDate, sDates, CultureInfo.InstalledUICulture, DateTimeStyles.None).ToString(sFormat)
Catch ex As Exception
Return String.Empty
End Try
End Function