1. Download the firmware image linked to above and the R4toR6_Prep_Addon.bin (26 KB) 2. Install the Prep add-on via Frontview e.g. via Add-Ons > Add New 3. Install the firmware image via System > Update > Local, reboot when prompted.
The Prep add-on will get the NAS to automatically do a factory default at the appropriate point. If you don't install the Prep add-on the NAS will get stuck at some point and you will need to power down and do a factory default via the boot menu