To increase the PHP Memory Limit do the following:
Step 1: Locate the wp-config.php file inside the root of your WordPress installation (located in the same folder as your /wp-content/ and /wp-admin/ directories) using an FTP client or file manager in your web hosting control panel (if you’re not sure how to do this, ignore the steps below and contact your web host who can do this for you).
Step 2: Paste this code in your wp-config.php file just before the line that says “That’s all, stop editing! Happy blogging.”:
define( 'WP_MEMORY_LIMIT', '128MB' );
Step 3: Now save the file.
Note: If this solution does not work then this means your web hosting service provider does not allow WordPress to increase PHP memory limit. You will need to ask your web host to increase this limit for you.