Hi,
first of all a good way to check if or where the file exists is to create a script
<?PHP
phpinfo();
?>
Near the top of the output you'll see the directory where php searches for php.ini.
If there isn't a php.ini at that location then you could download the source distribution if you're under unix or the binary version for e.g. windows if you're on windows because php.ini differs between those systems. Within the packages you'll fin sample php.ini files. Copy one of them to the location specified by the phpinfo() output and name it php.ini. Then edit it if you want to and restart the web server 🙂
Regards,
Thomas