The default location for the settings in apache 2.4 are: /etc/httpd/conf.modules.d/00-mpm.conf
<IfModule mpm_prefork_module> StartServers 5 MinSpareServers 5 MaxSpareServers 10 ServerLimit 25 MaxRequestWorkers 25 MaxConnectionsPerChild 0 </IfModule>Note: If ServerLimit is lower then MaxRequestWorkers then you will get the following error:
[root@apache ~]# httpd -t AH00180: WARNING: MaxRequestWorkers of 500 exceeds ServerLimit value of 256 servers, decreasing MaxRequestWorkers to 256. To increase, please see the ServerLimit directive. Syntax OK