On most Windows computers, updates are set to "automatic" by default, but it never hurts to double-check that you have the right settings in place.
In Windows 8, using a mouse, right-click in the lower right corner of the screen and choose Control Panel. If you're using a touch screen, swipe from the right of the screen and tap Settings>>Control Panel.
In Windows 7 and Vista, go to Start>>Control Panel.
In Control Panel, click System and Security and then under Windows Update click "Turn automatic updating on or off." Choose "Install updates automatically" in the drop-down menu.
You can choose when the updates will install. Updating usually restarts the computer, so try to pick a time you won't be using the computer, like during the middle of the day for your home computer or late at night for an office computer.
You will need to have your computer on at that time for the updates to happen. Click here to learn why shutting down your computer when you're not using it isn't a bad thing.
Note: If you have automatic updates turned on, but the updates aren't installed yet, you might see a yellow security icon on the Shut Down button in your Start menu. You can click the button to shut down and install the security updates right away.
When you're in the update settings, you'll also see the option "Include recommended updates when downloading, installing, or notifying me about updates." This will also install updates that aren't critical, but that Microsoft recommends.
Of course, even with automatic updates turned on, you might not be as secure as you think. When are automatic updates not really automatic? Click here to learn more.