Increasing memory allocated to PHP?

I need to increase the memory. However when I go to the wp-config there nothing there to increase the memory. I ‘ve been told to go to
https://codex.www.ads-software.com/Editing_wp-config.php#Increasing_memory_allocated_to_PHP
I don’t see the memory like this anywhere?
define( ‘WP_MEMORY_LIMIT’, ’64M’ );