Users of Windows will able to upgrade to the latest version of the operating system for free, says Microsoft. Windows 10 will be initially available for release for PCs and tablets, although you will need to be running the latest version of Windows 7 SP1 or Windows 8.1 update. And customers will be able to get an upgrade for free within the first year of release. Microsoft has promised Windows 10 will be faster than ever, work across different devices and bring…