Path.GetDirectoryName の もう１つ上の階層を指定

vb.net

LastIndexOf と LastIndexOfAny を使うとイイよ。

        Dim FilePath As String = "G:\sample1\sample2\sample3\test.txt"
        Dim UpDir As String = Path.GetDirectoryName(FilePath) 'G:\sample1\sample2\sample3
        Dim tempCount As Integer = UpDir.LastIndexOf("\") '18
        UpDir = UpDir.Substring(0, tempCount + 1) 'G:\sample1\sample2\

        'もう１つ上
        tempCount = UpDir.LastIndexOfAny("\", tempCount - 1) '10
        UpDir = UpDir.Substring(0, tempCount + 1) 'G:\sample1\