Changing php.ini settings on shared hosting depends on how php is installed on your server. I

phpsuexe mode - CGI

In this mode, php scripts run as the user.

Just make a copy of php.ini and put it on your public_html folder, php will use the php.ini


PHP as Apache Module

In this mode, php scripts run as nobody.

To override php.ini settings, you can try adding following to .htaccess file.


Code:
php_value upload_max_filesize 200M
php_value post_max_size 200M
php_value output_buffering on
php_value max_execution_time 2000
php_value max_input_time 2000
php_value session.gc_maxlifetime 24400
Now check your phpinfo to see the values are changed, if not contact your web host to see if they can change the php.ini for you.