You have to connect Via ethernet - then you can connect Via the wired IP and change the Wifi information...
![Smile :) :)](https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png)
On the Wall clock you can get to the RJ45 connector easilly at the underside of the unit itself (right side)... Just needs an RJ45 - RJ45 cable to hard wire - connect the other end to your Router ideally.
On the desktop it's a little more difficult as you need to take the front off - the sides will become loose, and by removing those you should be able to get access to the connector on the Pi.
In a perfect world if you know you are moving/changing providers, Set up the new wifi before the old one is disconnected/unaccessible. I completely get that it's not always possible though.