Series.PlotOrder (Excel)

Returns or sets the plot order for the selected series within the chart group.

You can set plot order only within a chart group (you cannot set the plot order for the entire chart if you have more than one chart type). A chart group is a collection of series with the same chart type. Changing the plot order of one series will cause the plot orders of the other series in the chart group to be adjusted, as necessary.

ActiveChart.FullSeriesCollection(1).PlotOrder = 3