From time to time when I try to upgrade an installation of WordPress I get an error that starts “Fatal Error: Allowed memory size of 33554432 bytes exhausted…” This means that WordPress needs a certain amount of space allocated to perform the upgrade, and the server is not allowing it. There are multiple options to fix this. The easiest is option #3 in the linked article. If you get an error while trying to edit your wp-config.php file, you probably need to CHMOD the permissions on the file to allow you to write changes to it.