How to: Remove a Chart Sheet
To delete a chart sheet from a workbook, remove it from the workbook’s ChartSheetCollection by using the ChartSheetCollection.Remove or ChartSheetCollection.RemoveAt method.
You can also move a chart back to the worksheet containing the source data by using the chart’s ChartObject.MoveToWorksheet method.
Worksheet worksheet = workbook.Worksheets["chartTask1"];
// Create the first chart sheet.
workbook.ChartSheets.Add();
// Create the second chart sheet.
workbook.ChartSheets.Add(ChartType.Pie, worksheet["B2:C7"]);
// Remove the first chart sheet.
workbook.ChartSheets.RemoveAt(0);