When you try to upgrade using the Application Manager and you get the "use Nokia PC Suite" error you might be able to press on the "details" button and there might be a "problems" button where there should be more information about the issue.
Résumé : "Cette mise à jour Maemo requiert Nokia PC Suite sur votre PC. L'application vous guidera pour la suite de la mise à jour Maemo." -- Problèmes : Impossible de mettre à jour Maemo 5 Community CSSU Package Conflit avec les paquetages d'application : custom-operator-name-applet Custom Operator Name Widget (0.1)
"Details: This Maemo update needs Nokia PC Suite on your computer. Le software will help you to update Maemo." -- Problems: "Maemo 5 Community CSSU Package's update impossible. Conflits with packets: custom-operator-name-applet Custom Operator Name Widget (0.1)