How to add last name of contact to its related account's name, when any contact field is updated using triggers?

you serach this question on my profile

trigger UpdateAccField on Contact (after insert,after update) {

List<Id> AccID = New List<Id>();
for(Contact con : Trigger.new){
if(con.AccountId != null){
AccID.add(con.AccountId);
}
}

List<contact> con = [SELECT Id,LastName, Account.Name, Account.Id FROM Contact WHERE Account.Id != null] ;
List<Account> acc = new List<Account>();
for(Contact s : Triger.new)
{
Account a = new Account();
a.Id = s.AccountId;
a.Name = s.Account.Name+s.LastName;
System.debug(‘aaa’+a.Id);
acc.add(a);
}
update acc;
}

Thanks