public int Update( int recordNo, string name, string number, string unn, string address )
{
    using ( var connection = new NpgsqlConnection( "Server=localhost;port=5432;user id=postgres;password=111111;database=postgres;" ) )
    {
        var command = new NpgsqlCommand( @"
            UPDATE eee.tab
            SET    Adress = @address,
                   Name   = @name,
                   Unn    = @unn,
                   VNum   = @number
            WHERE  NREC   = @recordNo", connection );

        command.Parameters.Add( "@address", NpgsqlDbType.Text, 50/*,"Adress"*/).Value = address;
        command.Parameters.Add( "@name", NpgsqlDbType.Text, 50/*,"Name"*/).Value = name;
        command.Parameters.Add( "@number", NpgsqlDbType.Text, 50/*,"VNum"*/).Value = number;
        command.Parameters.Add( "@unn", NpgsqlDbType.Text, 50/*,"Unn"*/).Value = unn;
        command.Parameters.Add( "@recordNo", NpgsqlDbType.Integer, 4/*,"NREC"*/).Value = recordNo;

        return command.ExecuteNonQuery();
    }
}

public int update(int NREC, string Name, string VNum, string Unn, string Adress)
{
    NpgsqlConnection conn = new NpgsqlConnection("Server=localhost;port=5432;user id=postgres;password=111111;database=postgres;");
    //string sqlcom = "update eee.tab set NREC=@NREC, Name=@name, VNum=@VNum,Unn=@Unn, "
    // + "Adress=@Adress where NREC=@ONREC;";
    NpgsqlCommand com = new NpgsqlCommand(@"update eee.tab set NREC=@NREC, Name=@name, VNum=@VNum,Unn=@Unn, "
+ "Adress=@Adress where NREC=@ONREC;", conn);

    com.Parameters.Add("@NREC", NpgsqlDbType.Integer, 4, "NREC");
    com.Parameters.Add("@Name", NpgsqlDbType.Text, 50, "Name");
    com.Parameters.Add("@VNum", NpgsqlDbType.Text, 50, "VNum");
    com.Parameters.Add("@Unn", NpgsqlDbType.Text, 50, "Unn");
    com.Parameters.Add("@Adress", NpgsqlDbType.Text, 50, "Adress");
    NpgsqlParameter param = com.Parameters.Add("@ONREC", NpgsqlDbType.Integer, 4, "NREC");
    param.SourceVersion = DataRowVersion.Original;

    try
    {
        conn.Open();
        return com.ExecuteNonQuery();
    }
    catch (SyntaxErrorException e)
    {
        throw new ApplicationException("error");
    }
    finally
    {
        conn.Close();
    }
}

com.Parameters.Add("@NREC", NpgsqlDbType.Integer, 4, "NREC");