Some website hosts will set a limit on the amount of memory WordPress can use, and this can cause certain issues. You will see some form of an error like this:
Fatal error: Allowed memory size of....etc.
The Easiest Method
Just ask your host to request increasing your memory limit – Let them know this is related to WordPress.
Editing Your Config File
Another method to fix this is to edit the wp-config.php file on your WordPress site. It is located in your WordPress site’s root folder, and you will need to use an FTP client or file manager in your web hosting control panel.
Next, you need to paste this code in that file just before the line that says “That’s all, stop editing! Happy blogging.”
define( 'WP_MEMORY_LIMIT', '256M' );
This code tells WordPress to increase the PHP memory limit to 256MB.
*If you have never edited a WordPress config file before, they have an article for reference.