Step 1 - Login to your WP site with an SFTP or FTP client
Login to your WordPress site with an SFTP or FTP client. We recommend Transmit (for Mac). FileZilla and Cyberduck are free options that is available for multiple platforms.
Step 2 - Locate the WordPress root
Then browse to your WordPress root or the current location of your wp-config.php file.
Step 3 - Add the WP_MEMORY_LIMIT constant to your wp-config.php file
Open your wp-config.php file with an editor. Next, copy one of the constants below and then paste it towards the middle of your wp-config.php file and save changes.
define('WP_MEMORY_LIMIT', '96M');
define('WP_MEMORY_LIMIT', '128M');
Video Tutorial
Click the play button on the video below:
References:
https://codex.wordpress.org/Editing_wp-config.php#Increasing_memory_allocated_to_PHP