Memory limit has been reached - magento 1.9

After migrating my magneto site to new server (CentOS 6 ) i can't update or upload new images to any of my products. its showing Memory limit has been reached while uploading any images.

logs :

2016-02-04T07:24:35+00:00 ERR (3): Notice: Undefined index: httponly in /var/www/vhosts/domain.com/httpdocs/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php on line 96
2016-02-04T07:24:35+00:00 ERR (3): Notice: Undefined index: httponly in /var/www/vhosts/domain.com/httpdocs/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php on line 96
2016-02-04T07:24:35+00:00 ERR (3): Notice: Undefined index: secure in /var/www/vhosts/domain.com/httpdocs/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php on line 98
2016-02-04T07:24:35+00:00 ERR (3): Notice: Undefined index: domain in /var/www/vhosts/domain.com/httpdocs/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php on line 100

For memory limit issue while uploading the product image, go to lib/Varien/Image/Adapter open Gd2.php

Now search for method protected function _convertToByte($memoryValue) i.e

protected function _convertToByte($memoryValue)
{
    if (stripos($memoryValue, 'M') !== false) {
        return (int)$memoryValue * 1024 * 1024;
    }
    elseif (stripos($memoryValue, 'KB') !== false) {
        return (int)$memoryValue * 1024;
    }

   return (int)$memoryValue;
}

Make the following changes in the above method like :

protected function _convertToByte($memoryValue)
{
     /*
     if (stripos($memoryValue, 'M') !== false) {
         return (int)$memoryValue * 1024 * 1024;
     }
     elseif (stripos($memoryValue, 'KB') !== false) {
         return (int)$memoryValue * 1024;
     }

     return (int)$memoryValue;
     */
     return 2147483648;
     //1024*1024*1024*2 = 2G
}