For further Informations see here: Check the installed firmware version
Right-click on the link to copy the link to your clipboard
Open the phone web interface, and navigate to the menu item "Software update."
Insert the copied link into the text field and press load.
(With Phone Manager)
The complete firmware update process may take a couple of minutes. Please do not interrupt the power supply to the phone during this process.
You can also update the firmware of Snom phones by means of auto provisioning. This allows you to update multiple phones simultaneously and with significantly less effort.
We explain how this works here: Firmware Update via Provisioning