I tried to update the themes and plugins in latest WorddPress 5.0 Gutenberg in DigitalOcean with Linux 18.XX with Apache . Before I install new plugin and Themes I tried to delete them. But WordPress was unable to processed. I researched and found that its ownership issue. The solve / fix this issue you need to perform following command in your command shell ( putty for Windows 10 in my case ).
chown -Rf www-data.www-data /var/www/html/
chown -Rf www-data.www-data /var/www/example.com/public_html
If that doesn’t work, alternatively you can try this command:
chown -R apache:apache /var/www/example.com/public_html
Replace “/var/www/example.com/public_html” with the path to where you actually have installed WordPress.