Suppressing PHP errors in admin panel

Hi folks,

[Disclaimer: I am new to CodeIgniter] I am trying to debug the PHP related warnings in this site: www.radhikavsharma.com. The warning is as follows:

      Strict Standards: Redefining already defined constructor for class MY_Model     in /data/18/3/19/41/3508204/user/3907478/htdocs/system/cms/core/MY_Model.php on line 79

The site was developed a while back by some web-developer and based on SO, I figured that I need to suppress the errors as follows in index.php:
The problem is that I cannot locate index.php in the admin panel. 

   error_reporting(E_ALL ^ E_STRICT);

Question: Which file can I modify (via the site's admin panel) to add the above error-suppression? Any guidance will be appreciated. Thanks!