Microsoft.Office.Interop.Excel.Application xlsapp = new Microsoft.Office.Interop.Excel.Application();
Microsoft.Office.Interop.Excel.Workbook workbook = xlsapp.Workbooks.Open(dlgSaveFile.FileName, 0, false, 5, "", "", true, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, Constants.vbTab, false,
false, 0, true, 1, 0);
Microsoft.Office.Interop.Excel.Worksheet sheet1 = workbook.Worksheets(1);
Microsoft.Office.Interop.Excel.Worksheet sheet2 = workbook.Worksheets(1);
To name your excel sheet,use the name property of your Work sheet object.
eg:
sheet1.Name="Example1";
sheet2.Name="Example2";
Happy coding..