=RIGHT(CELL("Filename",A1), LEN(CELL("Filename",A1)) - SEARCH("]",CELL("Filename",A1)))
Private Sub Worksheet_Change(ByVal Target As Range)
Dim strOldName As String
If Target.Address = "$A$1" Then
strOldName = Range("A1").Parent.Name
Sheets(strOldName).Name = Range("A1").Value
End If
End Sub