When upgrading Wordpress, a error messages occured “Fatal error: Allowed memory size of 33554432 bytes exhausted…"
If you spend some time googling for the solution, you'll find out that this error happened when execution of a php file exceed allowed php memory on the server. In this case, the allowed php memory is 33554432 bytes (32 Mb).
The solution is increasing allowed php memory, and you'll do that by editing wp-config.php file, adding right after “<?php”:
This increased allowed php memory to 128 Mb.