I have a trigger for Which I need to Write a Test Class.

Trigger:
 

trigger AccountShareWhenOwnerChage on Account (after update) {

        Set<Id> OwnerChangedAccs = new Set<Id>();
        
        for(Account a : trigger.new){
            if(trigger.oldMap.ContainsKey(a.id)  && a.ownerid != trigger.oldMap.get(a.id).ownerid){
              OwnerChangedAccs.add(a.id);
           }
        }
    
        List<AccountShare> lstAccShare = new List<AccountShare>(); 
    
        for(Account_Share__c aShare : [SELECT Id, Account__c, User__c FROM Account_Share__c WHERE Account__c IN :OwnerChangedAccs]){
            AccountShare as = new AccountShare();
            as.UserOrGroupID = aShare.User__c;
            as.AccountId = aShare.Account__c;
            as.AccountAccessLevel = 'Edit';
            lstAccShare.add(as);
        }
        insert lstAccShare;
    }
    
}

I have Written a Test Class for this  but it gives me only 60% code Coverage, Can you please help me in Increasing My Code Coverage
suggesting some changes.
 

@isTest
public class TestAccountOwnerChange{

    public static testMethod void unitTest(){
    
        Account a = new Account();
        a.name = 'Test Account';
        insert a;
        
         
        User u = new User();
        u.FirstName = 'Test';
        u.LastName  = 'User';
        u.Email     = 'testuser@gmail.com';
        u.Username  = 'testuser@gmail.com';
        u.Alias     = 'testy';
        u.ProfileId = '00ei0000001NKcq';
        u.TimeZoneSidKey    = 'America/Denver';
        u.LocaleSidKey      = 'en_US';
        u.EmailEncodingKey  = 'UTF-8';
        u.LanguageLocaleKey = 'en_US';
       
        insert u;
        
        Account ua = [SELECT Id,Name,Ownerid FROM Account WHERE Id = :a.id];
        ua.ownerid = u.id;
        update ua;
        
        
        Account_Share__c as = new Account_Share__c();
        as.Account__c = a.id;
        as.User__c = u.id;
        insert as;
        

        

        List<AccountShare> ashares = [SELECT Id, UserOrGroupId, AccountaccessLevel,

        RowCause FROM AccountShare WHERE AccountId = :as.Account__c AND UserOrGroupId= :u.Id];
        
        
        
        
        
        
        
     }

}

Thanks,
SFDC Beginner