Since I turned my DS409slim into a DS411j, I have access to DSM updates. So tonight, I upgraded from DSM 5.0-4528 Update 1 to 5.1-5004 using the update wizard. So far, everything went OK. On first reboot, I was recommended to keep my DSM up-to-date using automatic upgrade. As I don’t want my NAS to reboot while I’m working on it, I choose to “Download DSM updates but let me choose whether to install them”.
That’s all about it :)