public void UpdateBalance(int accountId, decimal amount)
{
    using (var connection = new SqlConnection("Your Connection String"))
    {
        connection.Open();

        using (var transaction = connection.BeginTransaction())
        {
            try
            {
                var command = new SqlCommand("SELECT balance, version FROM account_balance WHERE account_id = @accountId", connection, transaction);
                command.Parameters.AddWithValue("@accountId", accountId);

                using (var reader = command.ExecuteReader())
                {
                    if (!reader.Read())
                    {
                        throw new Exception("Account not found");
                    }

                    var currentBalance = reader.GetDecimal(0);
                    var currentVersion = reader.GetInt32(1);

                    reader.Close();

                    var newBalance = currentBalance + amount;
                    var newVersion = currentVersion + 1;

                    command = new SqlCommand("UPDATE account_balance SET balance = @balance, version = @version WHERE account_id = @accountId AND version = @currentVersion", connection, transaction);
                    command.Parameters.AddWithValue("@balance", newBalance);
                    command.Parameters.AddWithValue("@version", newVersion);
                    command.Parameters.AddWithValue("@accountId", accountId);
                    command.Parameters.AddWithValue("@currentVersion", currentVersion);

                    if (command.ExecuteNonQuery() == 0)
                    {
                        throw new Exception("The balance was updated by another transaction");
                    }

                    transaction.Commit();
                }
            }
            catch
            {
                transaction.Rollback();
                throw;
            }
        }
    }
}