How to delete a row from data base by selecting it,i'm using linq to sql inc# win forms ,along with sql server

public void btnDelete_Click(object sender, EventArgs e)
        {
            DMSDataContext db = new DMSDataContext();
            int userId = Int32.Parse(txtId.Text);
            User u = db.Users.Single(u1 => u1.Id == UserId); //here - how to get UserId from grid view?
            u.Id = Int32.Parse(txtId.Text);
            if (u != null)
            {
                db.Users.DeleteOnSubmit(u);
                db.SubmitChanges();
                MessageBox.Show("Record Deleted");
            }
            
      }