You can access every chart of a sheet using the Shape.Chart
property of a Sheet
object.
To change the name of each chart inside a sheet, use this macro:
Sub SetChartTitle()
Dim s As Shape
Dim i as integer
i = 1
For Each s In Sheets("Sheet1").Shapes
If s.HasChart Then
s.Name = "mychart" & i ' set the chart name
i = i + 1
End If
Next s
End Sub
You can even use this loop to export all your charts with s.Chart.Export