It's July 29, 2015 or later and Windows 10 is now available as a free update. Here is what you can expect when you say "yes" to the update.
As someone who signed up as a Windows Insider some months ago, I was near the top of the list for the free update to Windows 10. So, I took advantage of the situation and opted to get Windows 10 as soon as I possibly could. Here's a step-by-step walkthrough of the upgrade process I went through upgrading my Windows 8 machine to Windows 10.
Launch Windows 10 upgrade through Windows Update
I went to the Windows Update screen in Windows 8 and clicked the Check for Updates link. When the check was over, I was looking at the screen shown in Figure A.
As you can see, it is a decent size download. I clicked the Get Started button and then the screen shown in Figure B appeared.
You may be able to get Windows 10 via a free update, but it still requires that you agree to a license/user agreement.
The next screen (Figure C) is very important. Updating my Alienware M14x, with an Intel I7 CPU, 4GB RAM, nVidia GPU, and 350GB hard drive took every bit of two hours. If you cannot afford to be off your computer for that long, it may be a good idea to schedule a time when you can.
After you start the update process, your PC will immediately restart. From that point on you will just have to wait for the update to finish. During my update the screen was blank for over an hour, so please don't panic and turn your PC during this seeming lack of activity.
Your PC may also restart several times during the update, but eventually you will reach a screen that asks if you want to do an Express Configuration or a Custom Configuration. I opted for Express and it will be the best choice for most people.
Note that the update does take a bit of bandwidth, so it might be more efficient do update one PC at a time.
When the entire update procedure is complete, you will be presented with the Windows 10 desktop or tablet interface depending on your device. For me, it was the desktop, complete with my Skyrim wallpaper and all my previously installed applications, as you can see in Figure D.
I haven't had time to take a good look at everything, but I can already tell there are new versions of OneDrive and the Snipping Tool in Windows 10. Of course, there is also the new web browser, Microsoft Edge, too.
Get Windows 10 without using Windows Update
If you would like to get Windows 10 without going through the update process, for a clean install for example, then you will have to download the Windows 10 ISO file.
If you have a Windows Vista or Windows XP PC you would like to update, you have to purchase Windows 10. Windows 10 Home will cost you $119, while Windows 10 Pro will cost $199.
As of July 29, 2015, most new devices will be available with either Windows 10 or Windows 8.1, which can be upgraded to Windows 10 for free. If your PC is more than a few years old, it might make more sense to spend money on a new device rather than to update and old one.