Is there an easy way to change the existing value(s) of the ChartPoints in ChartWebControl?

You can access any of the points through the Series and Points collections:

The following Code simply demonstrate this.

C#

this.ChartWebControl1.BeginUpdate();

this.ChartWebControl1.Series[0].Points[0].X=1;

this.ChartWebControl1.Series[0].Points[0].YValues[0]=190;

this.ChartWebControl1.EndUpdate();