Need to reduce php workers

I need to reduce the number of php workers in virtualmin.

The server has about 10 websites on it of which 5 are wordpress.

ps ax --sort -rss -o rss,comm | head -n 10 produces the following output

172548 mysqld 158544 php-cgi7.3 157628 php-cgi7.3 129940 php-cgi7.3 109512 php-cgi7.3 92312 php-fpm7.0 92308 php-fpm7.0 92268 php-fpm7.0 89700 php-fpm7.0

How do i reduce php workers from virtualmin interface?