From the release notes:
" KNOWN ISSUES
UPDATE INSTALLATIONS SOMETIMES FAIL
Sometimes, after clicking on ‘Update and restart’ Daedalus will shut down, but the installation of the update will not start. If the user then tries to launch Daedalus within 60 seconds of Daedalus shutting down, the update will fail. The way around this problem is to wait for a minute after Daedalus shuts down and then start Daedalus manually. This will begin the installation process and avoid the problem.
Alternatively, the update can be made by downloading the latest installer from the Daedalus website and installing the new version of Daedalus manually. This will cure the problem."
By the way this happened to me as well. Wait a minute then start the wallet. Then it started the update process.