The free upgrade to Windows 10 has arrived. Here's what to expect.

Microsoft's Windows 10 is available as a free upgrade starting today for many users of Windows 7 or 8. Anyone who has the home or professional versions of Windows 7 Service Pack 1 or Windows 8.1 now has a year to take advantage of the offer. If you have plain Windows 7 or 8, you'll have to upgrade them first -- for free. Microsoft has more details about how to upgrade to Windows 10 here. But when it comes to operating systems, familiarity breeds contempt of change. A lot of consumers feel that if it ain't broke, stop touching my computer.