The httpd.conf file is owned by root. Therefore, in order to edit it, you'll need to do something like this:
Fire up the terminal and cd to where the httpd.conf file is (i.e. /etc/httpd/)
Now, to edit the file type "sudo pico httpd.conf" and enter your password. You can use vi or emacs or whatever you want if you don't like pico.
Edit the file and save your changes. Congrats! You have successfully edited the httpd.conf file.