Do It Yourself
To adjust on your own, here are some methods to try. Be aware that this section requires advanced knowledge; it is not basic.
Edit your wp-config.php file
Add this to the very bottom, right before the line that says, “Happy Blogging”:
WordPress memory can be different from the server – you need to set this regardless of server memory settings
Edit your PHP.ini file
If you have access to your PHP.ini file, change the line in PHP.ini
If your line shows 64M try 256M:
memory_limit = 256M ; Maximum amount of memory a script may consume (64MB)
Edit your .htaccess file
If you don’t have access to PHP.ini try adding this to an .htaccess file:
php_value memory_limit 256M
Contact Your Host
Should you not feel comfortable in trying the above methods, or the above did not work for you, you need to talk to your hosting about having them increase your memory limit.