Elasticsearch problem when update mapping

[Muhammad_Fhadli]

I want add mapping to synonym analyzer by perform this operation

PUT /my_index/_mapping/items
{
      "items": {
        "properties": {
          "judul": {
            "type": "text",
            "analyzer": "synonym"
          }
        }
      }
}

But, I got this error

{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "Mapper for [judul] conflicts with existing mapping in other types:\n[mapper [judul] has different [analyzer]]"
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "Mapper for [judul] conflicts with existing mapping in other types:\n[mapper [judul] has different [analyzer]]"
  },
  "status": 400
}

Here is my localhost:9200/my_index/_mapping/

{
  "my_index": {
    "mappings": {
      "items": {
        "properties": {
          .
          .
          .
          "judul": {
            "type": "text",
            "fields": {
              "keyword": {
                "type": "keyword",
                "ignore_above": 256
              }
            }
          },
          .
          .
          .
        }
      }
    }
  }
}

Can someone help me with this problem?
Please feel free to comment if you need more information, since I'm not really sure what else should i add in this description. Thank you

[dadoonet (David Pilato)]

You can't update an existing field and change the analyzer.

You need to DELETE the index and create it again.