Although the hard deadline to upgrade to Windows 10 has passed, this nifty article from How To Geek explains various ways you can still get it for free, some legally, some with slightly grey legality. Check it out if you missed out on the original upgrade window (pun intended).
Last Day for Free Upgrade to Windows 10
Today, July 29th, is the last day you can upgrade your Windows 7 or Windows 8.1 PC to Windows 10 for free. After today, Microsoft will presumably sell you the upgrade for a fee.
We recommend upgrading to Windows 10 for all home PCs. We recommend to our clients that new business workstations be bought with Windows 10. However, we do not recommend upgrading existing business workstations to Windows 10.
Another reason to upgrade to Windows 10
I'm a big fan of Windows 10, I've been using it for over a year. Microsoft has built in a handy tool to get your system fresh out of the box, but without all the bloatware that PC manufacturers get paid to deploy to you. This is a great innovation in my opionin. In the past when I've gotten a new PC, the first thing I have done is reinstall the OS fresh from scrath -- this tool will save a lot of time!
Here's the details: http://www.zdnet.com/article/microsoft-pushes-new-test-tool-to-kill-pc-bloatware/