You can’t, only the latest versions are available and it is not possible to roll back to a previous version.

What device/s are you having issues with?  Have you tried deleting the App and re-installing (being sure to connect to existing system).

The problem is that I'm using iMac mid 2007. I can't install 10.12 os. I can't imagine that Sonos doesn't have solutions for the previous version. At no time did I read that the new version was not compatible. If I had read that I wouldn't have updated.

The requirements for the Sonos App has always been stated here:

https://support.sonos.com/en-us/article/sonos-app-requirements

The partly supported older operating systems are listed here:

https://support.sonos.com/en-us/article/using-sonos-with-unsupported-operating-systems

If your OS is supported, or partly supported, then checkout the below information for Sonos App installation on a MAC PC…

Authorise the “Sonos Installer” under System Settings → Privacy & Security → App Management. Once allowed, you should be able to use auto update from the Sonos App itself to install the latest version of the Sonos App.

Hope that info. assists.

not really,
the automatic update having been carried out, even if this version is not compatible with my os. It is now too late to go back. And there are no solutions...

The Sonos auto-update feature will only update the device firmware only - you can of course disable auto-update at anytime and leave it disabled to prevent device updates.

Note too though that the App will continue update separately, but that is a separate setting on your mobile devices OS to disable App updates. For some operating systems it can be disabled for individual Apps, whilst others might involve switching off all mobile App updates. 

Yup, same here. I’m in 10.11.6 (that’s my maximum) and Sonos worked fine on the desktop
until I just updated to 15.2 yesterday and it won’t open. Amazing that there isn’t an archive of 15.1 somewhere. Sonos folks told me to call back tomorrow when they’re open. Not looking very good.

that's what I said high. incomprehensible on the part of sonos not to leave a version 15.1 archive. I am a developer and during our updates it is inconceivable not to leave an archive of the older installation

For Sonos the remote software version needs to be the same as the speaker software version. An older version of the app wouldn't work if the speakers have already updated.

Actually, it took a few calls/days, but the person at the call center emailed me a link to a download of 15.1.1 and it all works fine now. All else had been updated before (the iOS version, for example), to the latest - I suppose, the desktop version as well … until 15.2 threw a wrench into it.

Yes, it seems amazing that they don’t have an online archive of at least the last two or three versions at least. 

Yes but actually the speaker software is not up to date since the software on the computer is not launched

Not necessarily, there is an oft overlooked switch in the controller that allows automatic updating of the speakers. Settings > System > System Updates > Update Automatically. 

My speakers are version 15.3.

My Sonos app on my iPad is 15.3

My Sonos app on my desktop is (back to) 15.1.1.

All of it works great together now.

So, it was working great after I was able to get the older Sonos app - for the past couple of months.

NOW, even tho I’m still in 15.1.1 (while in the latest OS I’m allowed to have: 10.11.6), it began, three days ago, throwing up a black window saying that it wants to upgrade with no other option. So, I cannot use it any longer on my desktop.

Three calls to Sonos - the last one lasting nearly two hours - essentially saying, in the end, that I’m out of luck.
You would think that using an earlier version that worked with an older OS would just STAY working,
but NOOOOO…

Have your speakers updated?

Yes, 15.4

Then they are probably too far from the 15.1.1 on your controller. It might have been wiser to have stopped the speakers from updating automatically as pointed out above.

The automatic update is off, so I don’t know what happened.
Will a speaker factory reset remove the updates?

Factory reset just made it worse. The one speaker I tried it on just loaded 15.5 on it,
so one speaker is at 5 and the others at 4 - none of which I wanted. I’m getting rid of them.
Someone else can deal with the overriding authoritarianism of the company. 
There are plenty of other brands out there. Screw them.