- Plesk Onyx 17.5 for Linux
Will update of WordPress delete all changes made in WordPress files manually?
Update of WordPress instance should not delete any files, but all modifications made in any WordPress-related files will be replaced with defaults.
Regarding what happens to themes and plugins it is better to contact WordPress directly at https://wordpress.org/support/ . Plesk allows updating themes and plugins, but all actions performed withing WordPress installation are made on WordPress side and not designed by Plesk.