WP_MEMORY_LIMIT option was introduced in WordPress 2.5 to specify the maximum amount of memory that can be consumed by PHP. This is useful when you get a “memory exhausted” error message.
Option 1: Edit the WordPress Config File
Connect to your site via FTP and find the “wp-config.php” file in the root directory of WordPress. Now edit the “wp-config.php” file and enter something like:
define( 'WP_MEMORY_LIMIT', '64M' );
This will increase the PHP memory allocated for WordPress to 64MB. If you need even more you can set it to something like 256MB.
define( 'WP_MEMORY_LIMIT', '256M' );
Option 2: Edit the PHP Configuration File
This tweak may not do the full job since WordPress memory can be different to the server. In that case modify this value in your “PHP.ini” file (If your line shows 64MB try increasing the value to 256MB).
memory_limit = 256M ; Maximum amount of memory a script may consume (64MB)
Option 3: Edit the .htaccess File
If you don’t have access to the “PHP.ini” file you can try adding this to an .htaccess file.
php_value memory_limit 256M