We periodically release updates for Windows to include new features, the latest security protection, and the best drivers and software. Windows 8.1 Update and Windows RT 8.1 Update include improvements to make Windows more familiar and convenient for devices that use touch and mouse input and to make Windows available on a wider variety of devices, so you have more to choose from. Windows 8.1 Update and Windows RT 8.1 Update also include security and performance updates, and they must be installed for your PC to receive any future security updates for Windows 8.1 or Windows RT 8.1.
Getting the update
If you're already running Windows 8.1 or Windows RT 8.1, Windows 8.1 Update and Windows RT 8.1 Update are available for free through Windows Update. To see if you’re running the latest update, see Which Windows operating system am I running?
Otherwise, to install the latest update, see Install the latest Windows 8.1 Update