Once you grab the setup file you need, just double click on it and follow the on-screen instructions to apply the latest definitions to Microsoft Security Essentials.
The installer contains the complete, up-to-date anti-malware definitions for Microsoft Security Essentials, deploying the scanning engine (mpengine.dll), along with other files, such as mpasbase.vdm, mpasdlta.vdm, mpavbase.vdm, mpavdlt.vdm,
Windows will automatically download and install updates once a day for you.
There was one word that jumped out at me for being incorrectly spelled.
If your computer was asleep for a few days, or without internet connection, the files may be seriously outdated ("" - see the screenshot below, taken from the Update tab).
This tutorial shows you how to manually check for updates, and how to ensure that the program downloads any new files before running an automatic scan.
If you want Windows to update your software, go to Windows Update or: Because these updates change once a day, the definition version might be different to what is shown on this page, even after you've clicked the Update button.
Usually, updating once a day gives you a good level of protection, and it prevents us from constantly updating your software and interfering with how you use your PC. This can be helpful if you have hard-to-remove malware, Windows update isn't working properly, or you aren't always connected to the Internet.
This is the same as when Windows automatically downloads the update, and can be useful if you aren't always connected to the Internet or haven't turned your PC on for a few days.