Updating DJ-Classifieds can be done in various ways.
- You can use built-in update manager,
- you can simply install the latest AIO package from the download section and install it over the existing version (just install it like any other extensions - and DON'T uninstall the current version you're using),
- you can also use Joomla updater method.
Also, it's a good practice to backup your Joomla before updating any Joomla extension (just in case, to be secure). You can also check this article about updating extensions: https://dj-extensions.com/faq/general-faq/what-is-best-way-to-update-joomla-extensions
You can also check this article about updating extensions: What is the best way to update Joomla extensions.