Editing wp-config.php Increasing memory question

Sorry for noob question
Running php 5.4.39

I need to increase memory in wp-config.php to 256m
I see from reading the help files I need to add or modify:
define( ‘WP_MEMORY_LIMIT’, ‘256m’ );

I downloaded the file but can’t find that line anywhere to modify

Am I supposed to add this to the wp-config.php?
If so where in the file do I add it?
I understand the order is critical.

While we are on this topic can I also increase the current time limit from 240 to 300 in this same file?

Any help would be much appreciated.

Thank you
Scott