In the Visual Basic Editor, double-click ThisWorkbook under Microsoft Excel Objects in the Project Explorer pane on the left hand side.
Copy the following code into the ThisWorkbook module:
Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
If Not Intersect(Sh.Range("A1"), Target) Is Nothing Then
On Error Resume Next
Sh.Name = Sh.Range("A1").Value
End If
End Sub