Sub Macro1()
ScaleLinkedChart "Chart 4", 75
End Sub

Sub ScaleLinkedChart(strChart As String, lng_Size As Long)
'strChart is the chart name e.g. 'Chart 4'
'lng_size is the percentage of the original size e.g. 75 = 75%
Dim ofld As Field
Dim oShape As InlineShape
    For Each ofld In ActiveDocument.Fields
        If ofld.Type = wdFieldLink Then
            If InStr(1, ofld.Code, strChart) > 0 Then
                Set oShape = ofld.InlineShape
                oShape.ScaleHeight = lng_Size
                oShape.ScaleWidth = lng_Size
                Exit For
            End If
        End If
    Next ofld
lbl_Exit:
    Set ofld = Nothing
    Set oShape = Nothing
    Exit Sub
End Sub