You can make a variable to hold the latest date found and initialize it to the minimum value possible. Then you iterate over all the files and see if each one has a created date later than the date you've stored, and if so then you update the latest date and remember the filename, like this:
Dim dir As String = "C:\Parametre"
Dim latestFilename As String = ""
Dim latestDatetime As DateTime = DateTime.MinValue
Dim di As IO.DirectoryInfo = New System.IO.DirectoryInfo(dir)
For Each fi As IO.FileInfo In di.GetFiles()
If fi.CreationTimeUtc > latestDatetime Then
latestDatetime = fi.CreationTimeUtc
latestFilename = fi.FullName
End If
Next
' The variable latestFilename now contains the full name of
' the file with the latest creation date in the directory dir.
(Theoretically, although unlikely, there could be more than one file with the same latest creation timestamp, the above code will return only the first one that is recorded in the file system.)