DIAGNOSIS A failed update is almost always due to an unstable Wi-Fi connection during the process or a server-side glitch. The update gets corrupted and won't install.
FIX First, force a fresh attempt. 1) Close the Bose Music app completely on your phone (swipe it away). 2) Reboot your router and your phone. 3) Ensure your soundbar is on and connected (check in the app). 4) Re-open the app and go to 'Settings' > 'System' > 'Software Update'. If it fails again, you need to do a manual network refresh. Go to 'Settings' > 'System' > 'Network' and select 'Forget This Network'. Then set up the Wi-Fi connection again from scratch, making sure you're on that stable 2.4GHz band. After it's connected, try the update once more.
IF THAT DIDN'T WORK As a last resort, you can perform a full factory reset on the soundbar. Press and hold the 'Power' and 'Skip Forward' buttons on the soundbar itself (the touch-sensitive top panel) for 10 seconds until the light ring pulses amber and then turns off. This wipes all settings. You'll have to set it up like new in the app, but it often clears the update corruption.
HEADS UP Updates can be large. Make sure your phone isn't going to sleep during the process, and don't use other bandwidth-heavy apps (like streaming video) on your network while it's downloading and installing. Patience is key—it can take 15-20 minutes.