string query;
            query = "UPDATE tabFIO SET Prim = @Prim WHERE (Fam = @Fam) AND (Nam = @Nam)";
            
           conn.Open();

            SqlCommand cm = new SqlCommand(query, conn);

            SqlParameter prim = new SqlParameter("@prim", SqlDbType.VarChar);
            prim.Value = "Примечание - надо купить пива";
            cm.Parameters.Add(prim);
            .............
            cm.ExecuteNonQuery();