title: How to upgrade a running Elasticsearch older instance to a newer version?
body: <p>Essentially I cannot find documents or resources that explains the procedure of upgrading a running Elasticsearch instance into the current version. </p>
  
  <p>Please help me out in a few scenarios:</p>
  
  <ol>
  <li><p>If I am running an Elasticsearch instance in a single server, how do
  I upgrade the instance and not lose data?</p></li>
  <li><p>If I am running multiple Elasticsearch instances in a number of servers, how do I keep my operations running, while I upgrade my Elasticsearch instances without losing data?</p></li>
  </ol>
  
  <p>If there are proper procedures or explanations on this it will greatly help my understanding and work. Thanks!</p>