This was a bit more straight forward in the Apache 1.3 days since those directives were already included in the httpd.conf file. With Apache 2.0 and above that is not the case.
What you need to do is:
1. Open up your httpd.conf file.
2. Manually add the following lines right after the initial notes/messages are finished:
ServerLimit ####
MaxClients ####
3. Please replace #### in the above example with the actual number you wish to set. Be sure to keep ServerLimit *above* MaxClients so that apache parses it first, otherwise you'll keep getting the Alert upon httpd reboot. Make sure to keep your ServerLimit number equal to or higher than the MaxCllients number.
4. Restart apache after you have edited and saved the httpd.conf file.
Alternatively, you can put everything into the prefork.c module. Just copy/paste the following into the httpd.conf file and restart apache:
<IfModule prefork.c>
ServerLimit 1000
Timeout 25
KeepAlive On
MaxKeepAliveRequests 500
KeepAliveTimeout 15
StartServers 10
MinSpareServers 7
MaxSpareServers 15
MaxClients 800
MaxRequestsPerChild 1000
</IfModule>
Of course, adjust the above numbers to your liking.