Microsoft has officially released Windows 8.1 - an update to its Windows 8 operating system - during a keynote speech at its annual developers conference in San Francisco.

The free test version of the update is available to download now and the full version will be released to Windows 8 users later this year

The firm came under fire for its controversial ‘start screen’ in Windows 8, which gave users a series of tiles instead of a traditional desktop PC menu with a start button.

This left many confused, and caused a slower than expected uptake of the new software