Need help migrating an old Firebox SOHO 6 to a new account.

I have an old Firebox SOHO 6 that was happily running for years under the old administration account. However, I recently replaced all the units with newer models, but I would still like to use this on its own network. (isolated from the main network, as a failsafe more than anything)

The problem is, I would like to be able to upgrade the firmware to a newer version, however the machine's serial number is tied to the old administration account... Is there any way that I can migrate that to my account? The employee that managed it before is long gone.

Thanks everyone -- this is my first post here so I don't know what to expect!