550 Internal Server Error

Hi,
I have this problem:

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

I found this:
http://codex.gallery2.org/Gallery3:FAQ#I_get_an_error_500_when_I_visit_my_Gallery_3_install_for_the_first_time
I get an error 500 when I visit my Gallery 3 install for the first time

This probably means that your webserver doesn't support the "php_flag" command in the .htaccess file provided with Gallery 3. Solutions are:
1. edit your php.ini file and set "short_open_tag" to 1
2. edit your apache configuration file to allow per-directory overriding of Options or All (note that this has implications to broad to discuss here):
<Location "/gallery3/">
AllowOverride +Options
</Location>

Also, check to ensure that mbstrings are enabled within your php.ini file. Edit your php.ini file and ensure that "extension=php_mbstring.dll" is uncommented.

But i don't know where i found the file php.ini.I use Cpanel and i don't know where i edit "apache configuration file"

Can you help me?

Regards,
Mesquita