The easiest way to see if it is eligible is to add it to your account, and then log on to www.Sonos.com and look at your registered devices. That will give you the quickest indication as to whether or not the device is eligible for upgrade.

If they’re your own devices from new, you wouldn’t need to re-add them, they should still be on that page, and marked with a flag that says something like “upgrade available” or words to that effect.