Sub HeadersTest()
Dim oSection As Section
Dim oHeader As HeaderFooter
Dim oRng As Range
Dim strHeaderType As String
    For Each oSection In ActiveDocument.Sections
        For Each oHeader In oSection.Headers
            If oHeader.Exists Then
                Select Case oHeader.Index
                    Case 1: strHeaderType = "Primary"
                    Case 2: strHeaderType = "First Page"
                    Case 3: strHeaderType = "Even Pages"
                End Select
                Set oRng = oHeader.Range
                MsgBox "Section " & oSection.Index & vbCr & _
                       "Header " & strHeaderType & vbCr & _
                       "Contains: " & oRng.Text
                oRng.Text = "New header text for Section " & oSection.Index & " Header " & strHeaderType
                MsgBox "Section " & oSection.Index & " Header " & strHeaderType & " updated to " & vbCr & _
                       oRng.Text
            End If
        Next oHeader
    Next oSection
lbl_Exit:
    Set oSection = Nothing
    Set oHeader = Nothing
    Set oRng = Nothing
    Exit Sub
End Sub