title: Elasticsearch change field date format
body: <p>When i created my index and type a while ago I specified the date format of a field in the mapping as:</p>
  
  <pre><code>{"type": "date","format" : "dd/MM/yyyy HH:mm:ss"}
  </code></pre>
  
  <p>Is there a way to change the format of the field knowing that now i have more than 6000 docs indexed in my index ? I want the format to be:</p>
  
  <pre><code>{"type": "date","format" : "dd-MM-yyyy HH:mm:ss"}
  </code></pre>