There’s a few reasons why an update may get stuck like this. Generally it’s due to damaged files, interfering programs, permissions, or a connection issue. Let’s see if we can unstick this with the following:
First we’ll address corrupt files. I want to be thorough so what we’ll do is uninstall and reinstall Battle.net combined with removal of all cache and temp folder data. The steps here go over how to remove all files the Battle.net Application uses for installs and patches, and covers folders that are not removed with a basic uninstall. This way we ensure nothing related to the program is causing a problem:
1) Uninstall the application - https://battle.net/support/article/30304
2) Press Windows key + R and type in %temp%
3) Delete anything related to Blizzard or Battle.net
4) Do the same for %programdata%, %localappdata%, %appdata%
5) Reinstall the application! - https://battle.net/account/download/index.xml?show=bnetapp
Let’s see if creating and switching to a new Administrator Account helps. This sets many settings to defaults and also helps with permission problems, so can be useful to do even if you’re using an admin account already: Blizzard Support - Creating a New Administrator Account
Lastly is to target most connection or network issues. We do that by trying another network or connection entirely. That can be a friend’s or neighbor’s wifi. Many players have a hotspot or tether capability with their mobile devices which can also be used for testing.