
public class AcUpdate_Test{
public static testMethod void main(){
Account ac = new Account ();
ac.name = 'RBC WEALTH MANAGEMENT';
ac.Status__c = 'Active';
ac.SE2_Id__c = '25546';
ac.Channel__c = 'Bank';
insert ac;
ac.SE2_Id__c = '25346';
ac.name = 'RBC WEALTH MANAGEMENT1';
update ac;
Account ac1 = new Account ();
ac1.name = 'JJB HILLIARD LYONS';
ac1.Status__c = 'Active';
ac.SE2_Id__c = '25586';
ac1.Channel__c = 'Bank';
insert ac1;
ac.SE2_Id__c = '22546';
ac1.name = 'RBC WEALTH MANAGEMENT12';
update ac1;
Account ac2 = new Account ();
ac2.name = 'Test Account3';
ac2.Status__c = 'Active';
ac2.SE2_Id__c = '125456';
ac2.Channel__c = 'Bank';
insert ac2;
ac2.SE2_Id__c = '12546';
ac2.name = 'RBCSD WEALTH MANAGEMENT12';
update ac1;
Account ac3 = new Account ();
ac3.name = 'Test Account4';
ac3.Status__c = 'Active';
ac2.SE2_Id__c = '21254';
ac3.Channel__c = 'Bank';
insert ac3;
ac2.SE2_Id__c = '15256';
ac3.name = 'RBC WEALTH MANAGEMENT31';
update ac3;
Account ac4 = new Account ();
ac4.name = 'Test Account5';
ac4.Status__c = 'Active';
ac4.Channel__c = 'Bank';
ac2.SE2_Id__c = '8546';
insert ac4;
ac2.SE2_Id__c = '5740';
ac4.name = 'RBC WEALTH MANAGEMENT41';
update ac4;
}
}

Hi Anvesh,You need to prepare the data which will meet the conditions in the test class to get the complete coverage.In your data I see that no record has the value for SE2_Id__c field which is has the value in the trigger.Try the below code
Regards,Bhanu Mahesh@IsTest
public class AcUpdate_Test{
public static testMethod void main(){
Account ac = new Account ();
ac.name = 'TestAccount';
ac.Status__c = 'Active';
ac.SE2_Id__c = '20004';
ac.Channel__c = 'Bank';
insert ac;
Account acc = [SELECT Id,Name,SE2_Id__c FROM Account WHERE Id =:ac.Id];
System.assertEquals('RBC WEALTH MANAGEMENT',acc.Name);
acc.SE2_Id__c = '20002';
update acc;
Account acc1 = [SELECT Id,Name,SE2_Id__c FROM Account WHERE Id =:acc.Id];
System.assertEquals('JJB HILLIARD LYONS',acc1.Name);
Account ac1 = new Account ();
ac1.name = 'Test Account2';
ac1.Status__c = 'Active';
ac.SE2_Id__c = '20000';
ac1.Channel__c = 'Bank';
insert ac1;
Account acc2 = [SELECT Id,Name,SE2_Id__c FROM Account WHERE Id =:ac1.Id];
System.assertEquals('FTB ADVISORS INC',acc2.Name);
acc2.SE2_Id__c = '20005';
update acc2;
Account acc3 = [SELECT Id,Name,SE2_Id__c FROM Account WHERE Id =:acc2.Id];
System.assertEquals('BB&T SECURITIES LLC',acc3.Name);
Account ac2 = new Account ();
ac2.name = 'Test Account3';
ac2.Status__c = 'Active';
ac2.SE2_Id__c = '20003';
ac2.Channel__c = 'Bank';
insert ac2;
Account acc4 = [SELECT Id,Name,SE2_Id__c FROM Account WHERE Id =:ac2.Id];
System.assertEquals('KEY INVESTMENT SERVICES',acc4.Name);
}
}