When the Beam hasn’t been detected on your network for 72 hours, it will be removed automatically from the app. You can setup/add the Arc before the Beam has been removed.

If you plan on selling the Beam or giving it away, perform a factory reset first by following these steps:

https://support.sonos.com/s/article/1096?language=en_US

I get that, but still don't understand how on the S2 app where it gives me the remove option under system & system settings?

If I'm returning to store, is it imperative that I do a full reset or just remove it from my system? Thx

There is no remove option in the app. Just reset the Beam using the instructions in the link I posted, unplug the Beam from power, pack it in the original box, and return it to the store. When the Beam hasn’t been detected on your network for 72 hours, it will be removed automatically from the app. If you are impatient, you can force the Beam to disappear from the app sooner by rebooting all your other Sonos devices and your router, as well as force closing the app.

If you your problem is you want to give the Sonos "room” that contains the Arc to have the same name the Beam has now, rename the Beam-”room” before fysically removing it.