Ah, looks like I have found the answer :)

You can continue using your old products after upgrading. If you’d like to recycle your old products, our recycling article outlines options for responsibly recycling your Sonos products.

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Upgrade Program

This article will show you how to upgrade eligible Sonos products as part of our Upgrade program. See the FAQs on the Upgrade program home page for more information on eligible products and redeeming your credit.
 

1. Log in to your Sonos account

Log in to your Sonos account and navigate to the Upgrade section of the My Account page.
 

2. Choose products to upgrade

All eligible products will appear in the Eligible section. Check the box to the right of each product you wish to upgrade, then choose Upgrade at the bottom of the list. Your Sonos products must be plugged in and connected to your system in order to be eligible. You can view a list of eligible products on the Upgrade program home page.
 

3. Upgrade your product

You’ll receive a credit for each product you choose to upgrade. You can check your credit redemption status on the Offers section of the My Account page.
 

You can continue using your old products after upgrading. If you’d like to recycle your old products, our recycling article outlines options for responsibly recycling your Sonos products.

Sorry do you have to return old products and they will ship you new products

No, you keep your old products, and they continue to work as before, you just can’t use that product to get a second discount. 

Hi! I accidentally activated the upgrade for one of my speakers, is there a way to deactivate?

Not as I understand it. But why bother? Your speaker will keep on working.