Delete files older than dayofyear

In my code below I am getting the newest file in a folder
Then setting day of year variable(dtYear) from that files last write time

What I would like to do is delete all files in that folder OLDER that dtYear - 2
So that I always have three days of files in the folder.

Private Sub getFiles()
        Try
            Dim appPath As String = Application.StartupPath
            Dim strPath As String
            strPath = File.ReadAllLines(Path.GetFullPath("directorypath.txt")).First() '"C:\Program FIles\"
            Dim di As New System.IO.DirectoryInfo(strPath)
            Dim files As New List(Of System.IO.FileInfo)
            files.AddRange(di.GetFiles())
            files.Sort(AddressOf SortFilesDescendingByLastWriteTime)
            Dim newestFile As System.IO.FileInfo = files(0)
            Dim dtYear = newestFile.LastWriteTime.DayOfYear
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub

    Private Function SortFilesDescendingByLastWriteTime(ByVal fiA As System.IO.FileInfo, ByVal fiB As System.IO.FileInfo) As Integer
        Return fiB.LastWriteTime.CompareTo(fiA.LastWriteTime)
    End Function

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