A template plugin previously written for ckan 2.8.2 version does not work stable in ckan version 2.9.5. Are there any ways to update it for ckan 2.9.5? Or do I need to update the template manually ?
Upgrading from CKAN 2.8.x to 2.9.x is a minor version release but still contains backward-incompatible changes and a major change from Python 2 to Python 3 and Pylons to Flask.
First, you can go over the Changelog and see what has been changed in the new releases. Then, go over the Python 3 migration guide https://github.com/ckan/ckan/wiki/Python-3-migration-guide-for-extensions and start updating the required changes.