Here is MicroSoft’s link on it. The website states that if you have your updates set to automatically install, you may already have this installed.
YMMV, but in my experience, this was not the case. If you do not install this update, MicroSoft will not install any future updates on your system. There was a prerequisite update that did not install correctly on another system I worked with. The end result was that in both cases, intervention was required for a successful install.
First things first, this update is large. It is about 700 MB in size. I know this is not as big as the 8.0 to 8.1 upgrade which was about 3.5 GBs, but the download and installation of this update is time consuming. If your habit is to turn on your computer only when you need it, you are looking at a considerable amount of time just to prepare your system for the update. I suggest that you do this starting in a morning that you are not going to work, where you can monitor the progress and you can stay off of your system for about 4 hours. For me, this was a Saturday morning. I was done by lunch.
Connect your power supply. Close all open programs. Go to PC settings, Update and recovery Windows Update and click on <Check Now>. After the repository of information is updated, then select View details. Look for KB 2919355. This is the update you need to install. On my system, it was in the optional updates. Go ahead and trigger the install. Leave the system on in a place where you can monitor it and check on it frequently. If it fails, you want to know as soon as possible when it fails so that you can try again.
On one system I upgraded, I had to identify a prerequisite that had failed to install. This information can be found by viewing your update history. You will probably want to download the frozen updates directly from the Microsoft download center. You can then search for the update by it’s KB number (KB = Knowledge Base).
Once downloaded, install the frozen downloads individually. You may have to reboot in between the installs. If you run into trouble with installing an update, search Microsoft TechNet for the KB number and begin reading. You may want to read other blogs/forums that cover this information, but DO NOT INSTALL ANY HACKS FROM 3RD-PARTY WEBSITES. They may or may not work, and they very well may be malicious.
After all the updates have been installed, return to Windows Update and check again for additional updates. Repeat this process until all updates are installed. Don’t forget to reboot after the final update is installed, and then have your favorite adult beverage.