Users have reported some problems upgrading WordPress from 2.4 -> 2.5 on Blinkenshell. The problem seems to be that the upgrade script requires a lot of memory, more than the limit at Blinkenshell. Normally you can change this in your PHP script yourself, but since we use Suhosin for PHP this setting is locked down. I’ve now reconfigured Suhosin to allow users to set the memory limit up to 16MB (instead of 8MB.) I’ve now myself tried upgrading WordPress and it seems to have worked.
I followed the basic instructions here: http://codex.wordpress.org/Upgrading_WordPress
However, I had to change WP_MEMORY_LIMIT in wp-settings.php from 32MB to 16MB. Also, I had to redo the fix for canonical redirects (Howto WordPress.) The problem with canonical redirects might get fixed in 2.6, atleast that’s what the ticket in their bugtracking system said.