elasticsearch/docs/reference/upgrade/remove-xpack.asciidoc

IMPORTANT: If you are upgrading from 6.2 or earlier and use {xpack},
run `bin/elasticsearch-plugin remove x-pack` to remove the {xpack} plugin before
you upgrade. The {xpack} functionality is now included in the default distribution
and is no longer installed separately. The node won't start after upgrade if
the {xpack} plugin is present. You will need to downgrade, remove the plugin,
and reapply the upgrade.