DELETE * FROM Portfolio WHERE PortfolioID = @PortfolioID

<asp:GridView ID="myGrid" runat="server" DataKeyNames='PortfolioID' OnRowCommand="dgStudent_RowCommand">
    <Columns>
        <asp:ButtonField ButtonType="Button" CommandName="Delete" Text="Delete"></asp:ButtonField>
    </Columns>
</asp:GridView>

protected void myGrid_RowCommand(object sender, GridViewCommandEventArgs e)
{
    // create and open DB connection
    int PortfolioID = (int)myGrid.DataKeys[Convert.ToInt32(e.CommandArgument)].Value;
    DeleteRow(PortfolioID); // your implementation
    myGrid.DataBind();
}

private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
    {

        this.txt_portfolioId.Text=dataGridView1.CurrentRow.Cells["portfolioID"].Value.ToString();


    }


private void btn_Delete(object sender, EventArgs e)
    {

        //You need to connect to database(regular database connection this connection string and sqlcommand and add this sqlquerry: