I am getting below error while I click on
Delete word under name of a plugin.
Wordpress will popup for FTP credentials if it does not have permission to write the files it needs to. Am assuming your WordPress website is hosted on Linux OS. And also if you connected to your server using SSH (i.e., putty, etc.). Please try to run the below command:
sudo chown -R www-data:www-data /var/www/html
Alternate Method: Try to define below the line in wp-config.php. But this could create security issues.