how to edit and delete items from gridview rows without using database

protected void btnAdd_Click(object sender, EventArgs e)
{



if (Session["Data"] == null) //Checking if the session contain any value.
{
DataTable dt = new DataTable(); //creating the columns.
dt.Columns.Add("Course");
dt.Columns.Add("Mark");
dt.Columns.Add("Percentage");
dt.Columns.Add("CourseCompletedYear");
DataRow dr = dt.NewRow(); //Create a new row and add the row values.
dr[0] = ddlCourse.SelectedItem.Text;
dr[1] = txtMark.Text;
dr[2] = txtPercentage.Text;
dr[3] = txtCourseCopmYear.Text;
dt.Rows.Add(dr);

GridViewCandidate.DataSource = dt; //Populate values to Gridview.
GridViewCandidate.DataBind();

Session["Data"] = dt; //Storing that table into session.
}
else
{
DataTable dt = new DataTable();
dt = (DataTable)Session["Data"]; //Retrieve the stored table from session.

DataRow dr = dt.NewRow(); //Adding a new row to existing table.
dr[0] = ddlCourse.SelectedItem.Text;
dr[1] = txtMark.Text;
dr[2] = txtPercentage.Text;
dr[3] = txtCourseCopmYear.Text;
dt.Rows.Add(dr);

GridViewCandidate.DataSource = dt; //Populate new table values to Gridview.
GridViewCandidate.DataBind();

Session.Remove("Data"); //Clear the session.
Session["Data"] = dt; //Store the new table to the session.
}

how can i remove row from the gridview.?