How to modify the format of a chart in a CrystalReport?

C# asp.net
There is a chart in one of my CrystalRepot document. I can control the text of a TextBox very easily. like this:
TextObject GetTextObject;
GetTextObject=(TextObject)person_list.ReportDefini tion.ReportObjects["Text21"];
GetTextObject.Text="something";

But,how to change the mode of the chart? e.g: pie to bar? and how to change the condition of the group?(e.g:change the group condition from sex to location.)
all in code.
thanks!

Rtfm

thanks,but could you tell me in detail?