Updating WordPress on Plesk Onyx
WordPress, its Theme and plugins need to be kept updated as vulnerabilities are discovered on a regular basis, and hackers are scanning the internet for vulnerable web sites to exploit.
You will fin a good write up about Upgrading WordPress on the WordPress Codex:
https://codex.wordpress.org/Upgrading_WordPress_-_Extended_Instructions
Here is a link to the procedure we recommend for Updating WordPress and its components (Plugins, Themes).