Sometimes when you update WordPress there will be an interruption and you will be greeted with the following error message:
“Briefly unavailable for scheduled maintenance. Check back in a minute.”
The good thing about this is that its an easy fix but can be caused by a couple of issues.
Firstly, start a new browser session, clear your cache and then try and hit the ‘update WordPress’ button again in the admin area. This can fix the issue.
If that fails to work it could be because a .maintenance file has been left in the root directory of your server. It usually gets deleted automatically but because of the interruption it may still be there.
Visit your website files via FTP and then delete the .maintenance file if appears in your root directory.
These two methods should have you back up and running, but if not you might have to download the latest version of WordPress from the official website and then upload the new files via ftp.
Good luck and I hope this helped!