How to know elastic search installed version from kibana?

I would like to add which isn't mentioned in above answers.

From your kibana's dev console, hit following command:

GET /

This is similar to accessing localhost:9200 from browser.

Hope this will help someone.

from the Chrome Rest client make a GET request or curl -XGET 'http://localhost:9200' in console

rest client: http://localhost:9200

{
    "name": "node",
    "cluster_name": "elasticsearch-cluster",
    "version": {
        "number": "2.3.4",
        "build_hash": "dcxbgvzdfbbhfxbhx",
        "build_timestamp": "2016-06-30T11:24:31Z",
        "build_snapshot": false,
        "lucene_version": "5.5.0"
    },
    "tagline": "You Know, for Search"
}

where number field denotes the elasticsearch version. Here elasticsearch version is 2.3.4

You can check version of ElasticSearch by the following command. It returns some other information also:

curl -XGET 'localhost:9200'

{
  "name" : "Forgotten One",
  "cluster_name" : "elasticsearch",
  "version" : {
    "number" : "2.3.4",
    "build_hash" : "e455fd0c13dceca8dbbdbb1665d068ae55dabe3f",
    "build_timestamp" : "2016-06-30T11:24:31Z",
    "build_snapshot" : false,
    "lucene_version" : "5.5.0"
  },
  "tagline" : "You Know, for Search"
}

Here you can see the version number: 2.3.4

Typically Kibana is installed in /opt/logstash/bin/kibana . So you can get the kibana version as follows

/opt/kibana/bin/kibana --version