Increasing your wp_memory_limit is easy to do, as are all things once you know what to do.
Go into the cPanel for your site's server, then open up the File Manager. Double click on Public HTML, then look for a .php file called wp_config.
Normally, I would caution you to make and save a copy of the whole unedited file to your desktop before-hand and this is a good habit and practice to follow. However for something this simple I no longer do this myself. Yes I probably should.
Right click on wp_config and open it for editing.
Now scroll down in the file until you find this line;
define('WP_DEBUG', false);
Directly under this line place the following line of code;
define('WP_MEMORY_LIMIT', '768M');
Most important step
Save the file.
That's it. You have just successfully increased your wp_memory_limit.