Hello Hami,
The admin password has to be changed via command line, it is not possible to change it from the GUI. To do so follow these steps:
1. Replace <new-password> and generate a hash for it using the hash.sh utility from Open Distro for Elasticsearch:
bash /usr/share/elasticsearch/plugins/opendistro_security/tools/hash.sh -p <new-password>
2. Open the file /usr/share/elasticsearch/plugins/opendistro_security/securityconfig/internal_users.yml and edit the section for the user admin where you need to replace the old hash with the newly generated one:
admin:
hash: "<newly_generated_hash>"
reserved: true
backend_roles:
- "admin"
description: "Demo admin user"
3. Execute the securityadmin script so these changes can take effect:
cd /usr/share/elasticsearch/plugins/opendistro_security/tools/
./securityadmin.sh -cd ../securityconfig/ -nhnv -cacert /etc/elasticsearch/certs/root-ca.pem -cert /etc/elasticsearch/certs/admin.pem -key /etc/elasticsearch/certs/admin.key -h localhost