As July winds down, so does Microsoft’s offer to upgrade most of its existing users to Windows 10 Home for free. The free upgrade ends July 29 at 6 p.m. Denver time, after which Windows 10 will cost about $120. So far, roughly 350 million devices that have taken Microsoft up on the offer, which is triple the number of devices from October, though far from its goal of 1 billion devices. But the freebie, as many readers know, wasn’t without headaches.