Fatal Error

I get this error:

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 30720 bytes) in /data/9/2/75/132/2727458/user/2997114/htdocs/wp-admin/includes/menu.php on line 174

I know I need to increase something by inputting this:
define(‘WP_MEMORY_LIMIT’, ’64M’);

But, I have absolute ZERO EXPERIENCE and dont know where Im looking to write/input this data (define(‘WP_MEMORY_LIMIT’, ’64M’);)?

Any help as to WHERE I go to do this would be so much appreciated!