Select Choose how updates get installed, and then, under Important updates, select Install updates automatically (recommended). If you want to check for updates manually, select Check now.

Open Windows Update by swiping in from the right edge of the screen (or, if you're using a mouse, pointing to the lower-right corner of the screen and moving the mouse pointer up), select Settings > Change PC settings > Update and recovery > Windows Update. Instead, Windows Update automatically installs important updates as they become available. With automatic updates, you don’t have to search for updates online or worry about missing critical fixes or device drivers for your PC.

The best way to keep Windows 8.1 up to date is to turn on automatic updates. Note: If you're looking for Microsoft Office update info, see Install Office updates.