Why Do You Need An Upgrade?
A WordPress blog gets several updates periodically. The upgrade is necessary for the following reasons.
If we are not careful about the upgrade, it can give us a hard time. It will be a nightmare for developers especially if the website has a large number of plugins. After the upgrade when you browse the website you may be shocked to find several errors due to reasons arising from breaking the plugin, theme compatibility with the new version and so on. Another reason for the errors can be due to the server upgraded to the latest PHP version.
So the safest way to avoid such a difficult situation is to have a development server with the same environment ready by cloning the production server. First, perform a WordPress upgrade on the development server. If you find any errors with the plugin or theme, contact respective developers for a compatible version. The problem arises when the original developers are not available. You have to change the code all by yourself. Resolve the development server errors one by one by troubleshooting the plugin and the theme issues. Note down the changes you are making at the code level to repeat them in the production server.
Before doing the upgrade on the production side, have a backup of the database in case of any unexpected errors. In my experience, most of the errors are coming from the plugin side.
I have found a very nice blog post https://www.searchenginejournal.com/how-to-update-wordpress/282117/#close on the wordpress upgrade that describes the best approach.