c# replace email template

Email email = new Email
                    {
                        To = new ActivityParty[] { toParty },
                        From = new ActivityParty[] { fromParty },
                        Subject = "SDK Sample e-mail",
                        Description = "SDK Sample for SendEmailFromTemplate Message.",
                        DirectionCode = true
                    };



QueryExpression queryBuildInTemplates = new QueryExpression{
                        EntityName = "template",
                        ColumnSet = new ColumnSet(true),
                        Criteria = new FilterExpression()
                    };
                    queryBuildInTemplates.Criteria.AddCondition("title",
                        ConditionOperator.Equal, "test");
                    EntityCollection templateEntityCollection = _serviceProxy.RetrieveMultiple(queryBuildInTemplates);

                    if (templateEntityCollection.Entities.Count > 0)
                    {
                        _templateId = (Guid)templateEntityCollection.Entities[0].Attributes["templateid"];
                    }
                    else
                    {
                        throw new ArgumentException("Standard Email Templates are missing");
                    }

                    // Create the request
                    SendEmailFromTemplateRequest emailUsingTemplateReq = new SendEmailFromTemplateRequest
                    {
                        Target = email,

                        // Use a built-in Email Template of type "contact".
                        TemplateId = _templateId,

                        // The regarding Id is required, and must be of the same type as the Email Template.
                        RegardingId = _contactId,
                        RegardingType = Contact.EntityLogicalName
                    };

                    SendEmailFromTemplateResponse emailUsingTemplateResp = (SendEmailFromTemplateResponse)_serviceProxy.Execute(emailUsingTemplateReq);