How to update excel embedded charts in powerpoint?

If you need to edit the charts then clearly you will either need to edit the underlying Excel files, or be able to edit in PowerPoint

As you are using PowerPoint2007 which provides full Excel support (unlike PowerPoint 2003 which has a datasheet) I would

Part 1

1. Link your Excel file data to the Excel data underneath each chart
2. Provide the ability to either use that data directly, or over-ride it with user data

This gives you a flexible solution, except that Excel underlying each chart cannot be updated automatically via a PowerPoint menu Update Links command.

Part 2

You can use the code below to test each whether each shape on each slide has a chart. If so this code will update the first Excel link in the Excel file underneath the chart (this part can be tweaked to handle multiple links)

    Sub ChangeChartData()

    Dim pptChart As Chart
    Dim pptChartData As ChartData
    Dim pptWorkbook As Object
    Dim sld As Slide
    Dim shp As Shape

    For Each sld In ActivePresentation.Slides
        For Each shp In sld.Shapes
            If shp.HasChart Then
                Set pptChart = shp.Chart
                Set pptChartData = pptChart.ChartData
                pptChartData.Activate
                Set pptWorkbook = pptChartData.Workbook
                On Error Resume Next
                'update first link
                pptWorkbook.UpdateLink pptWorkbook.LinkSources(1)
                On Error GoTo 0
                pptWorkbook.Close True
            End If
        Next
    Next

    Set pptWorkbook = Nothing
    Set pptChartData = Nothing
    Set pptChart = Nothing

End Sub

This is fairly easily accomplished, without any VBA code required.

1. Click the "Office Button", select "Edit Links to File" (it's beneath "Run Compatibility Check", you will have to scroll down to see that last option):

   

2. Select all embedded charts (referred to here as "links"), click "Update Now":

   

You can use the same window to break links, as well as to change the source file for any given link.