Excel and VB.net Question?

Hi, I'm making a program to save data to excel file. I've accomplished saving the DataGridView I'm using to a Excel File. My question is "Can you save a excel file without overwriting the previous information on the excel file?" In other words can I just update the excel file?

here's my code...

        Dim xlApp As Excel.Application
        Dim xlWorkBook As Excel.Workbook
        Dim xlWorkSheet As Excel.Worksheet
        Dim misValue As Object = System.Reflection.Missing.Value
        Dim i As Integer
        Dim o As Integer

        xlApp = New Excel.Application
        xlWorkBook = xlApp.Workbooks.Add(misValue)
        xlWorkSheet = xlWorkBook.Sheets("sheet1")

        For i = 0 To dgvRecentOrders.RowCount - 2
            For o = 0 To dgvRecentOrders.ColumnCount - 1
                xlWorkSheet.Cells(i + 1, o + 1) = dgvRecentOrders(o, i).Value.ToString()
            Next
        Next

        xlWorkSheet.SaveAs("C:\testexcel.xlsx")

        xlWorkBook.Close()
        xlApp.Quit()

Thanks in advance!