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