Solution:
To increase memory you can do it with wp-config.php.
Administration tasks require much memory than usual operation. When in the administration area, the memory can be increased or decreased from the WP_MEMORY_LIMIT by defining WP_MAX_MEMORY_LIMIT.
define( 'WP_MAX_MEMORY_LIMIT', '512M' );
define('WP_MEMORY_LIMIT', '256M');
note, this has to be put before wp-settings.php inclusion.
With php.ini
memory_limit = 256M ;
With .htaccess
php_value memory_limit 256M
It could be great to upgrade some other values like set_time_limit (that returns error when reached) and max_execution_time