The download seeks to address some of the criticisms levelled at the original version of Windows 8.
In particular, the update restores the start button and allows a computer to boot up with a traditional desktop interface.
The launch comes at a critical time for Microsoft as it seeks a new boss, with PC sales experiencing a long decline.
Windows 8 sought to bridge the gap between touchscreen devices, such as tablets and smartphones, and more traditional form laptops and desktop machines. As such it had an interface built of tiles that could be tapped or swiped to open applications.
However, many people found the tiled interface did not work well for some of the things they were used to doing with a computer.
The changes in 8.1 include:
start button - tapping once on this brings up the tiled interface and a long press opens up system controls
desktop mode - lets people avoid the tiled interface entirely
keyboard shortcuts - removes the need to toggle between different on-screen keyboards when typing numbers and letters
gesture control - some applications, such as those for cooking, can now be paged through without touching a screen
tile sizing - the blocks on the touchscreen interface can be in one of four sizes
web browsing - Windows 8 machines will now display separate web pages side by side
A host of other changes, including better support for multi-tasking and improved links to Microsoft's Xbox game console, are also in the update.
