error when trying to install version 3.5

Hello,

I’m trying to upgrade to version 3.5, but get the following error message:
Téléchargement de la mise à jour depuis https://fr.www.ads-software.com/wordpress-3.5-fr_FR.zip…

Décompression de la mise à jour…

Warning: copy(/homepages/22/d394431025/htdocs/app394431044/wp-admin/includes/update-core.php) [function.copy]: failed to open stream: Permission denied in /homepages/22/d394431025/htdocs/app394431044/wp-admin/includes/class-wp-filesystem-direct.php on line 200

Impossible de copier les fichiers.

échec de l’installation

From what I read this is a file permission issue. So downloaded filezilla, tried changing the file permission for the update-core.php file. But it won’t let me……. operation not permitted.

What else can I try?

Thanks
Karine