Are you on the phone/tablet app? If so, the path is:

Settings [cog symbol] - Manage - System Updates - Check for Updates.

If you change your wifi name and password to the old ones all should work. 

Thanks, but the Manage option in System settings is not highlighted and not possible to click.

I use the app from my phone or tablet and it’s the same for both 

In which case, the best route is to use the desktop app for Windows or Mac, available here (or your local site for this):

https://support.sonos.com/en-gb/downloads

This is often recently used to update the system where the phone is unable to, as it is built similar to the old app. Try installing on your laptop, then go to the top bar menu to Check for Updates. 

Many thanks Ronny! After downloading on my computer and from there doing the upgrade the system is now back again! Very frustrating I have to say so I am very thankful for your help. Regards Lena