If you do an update on one of your Apple network devices, like a Time Capsule or AirPort Extreme, and then you find that you’re having problems afterward, what do you do? Well, don’t freak out. (That’s always my recommended first step.) But after you commence not freaking out, then consider downgrading the firmware on the offending device. Unlike with macOS and iOS, Apple provides a really simple way to do this for network devices using the AirPort Utility program. So if you find that printing’s spotty or an older device won’t connect, this’d be an easy troubleshooting step, especially if you can link the start of the trouble to an upgrade you installed!
So to do this, first open AirPort Utility. That program lives in your Applications folder in a subfolder called (surprise!) Utilities, a shortcut for which lives under Finder’s “Go” menu.
Once you’ve got AirPort Utility running, you should see your available Apple networking devices appear in the window (and if you don’t, be sure you’re on your home network and not, say, a neighbor’s or the godawful xfinitywifi one).
When you click on any device and enter its password, you’ll be given a list of its basic info.
Here’s where the magic happens—if you Option-click on the version number shown there, you can revert back to a previous one really quickly.
When you pick the firmware version you want, AirPort Utility will warn you that your device is about to go offline, of course.
Then just wait for the installation process to complete, and you’re done! If you decide that you’d like to give the problematic version another try at some point, all you have to do is go back to AirPort Utility. You’ll see that option available to you again on the selected device.