changing the connection string in SQL Server
After SSIS package deployed to new environment still it may use old connection string. 


  how to change the connection string i.e initial catalog or server name
  parameter from Agent job > configuration > connection manger .Is there
  a possibility to do from here ?


Yes, It's possible when you are sysadmin and you can change manually by following: 


  Right click on AgentJob -> Properties -> Job step -> Configuration ->
  Connection Managers 
  
  Below Connection Managers -> select Name of database then on
  properties -> 
  
  
  Connectionstring -&gt; Data Source=yourServerName;InitialCatalog=Databasename;Provider=SQLNCLI11.1;IntegratedSecurity
  = SSPI;Auto Translate=False; (you can edit Data source and intial catalog manually) 
  
  
  and 
  
  
  Servername = 'yourservername'