You can place a file called "php.ini" in the root folder of your site (public_html) or you can place a file called ".htaccess" in the highest folder of the section of the site you want to affect.
php.ini is the preferred way, .htaccess is limited under suexec - see
PHP SuExec Explained (previously posted)
Also see the "PHPsuexec" section of
https://desk.surpasshosting.com/inde...barticleid=176
Also:
for php.ini
PHP: Runtime Configuration - Manual
PHP: Description of core php.ini directives - Manual
for .htaccess
PHP: How to change configuration settings - Manual (is written for Apache module configurations, some of this applies to suExec installs...)