I noted that with OS 14.12 that 5GHz WiFi is supported on my older Play:1
Stupidly I went ahead with trying to change network settings.
The mobile app just wouldn't prompt to change or add settings in Manage Networks → Update Networks, even after deleting the existing network and connecting by wired, it just kept on looping round not finding the Sonos (as is mentioned in other threads here - as well as prompting to enable Bluetooth).
I started to worry I’d never get wireless working again, in the end I factory reset the Sonos (hold Play button while powering on) and luckily the mobile app then did find the Play:1 and prompted to connect to the 5GHz SSID straight away.
But the reset lost all settings, services, favourites, connections to the library, to Alexa, everything in fact, so a simple network change ended up taking hours of work.