But how do you get it? And what do you need? We'll tell you very soon....
Windows 10 system requirements
Firstly, you must check that your PC exceeds the system requirements. Mind you, if it doesn't you're obviously using something so ancient that you need a new PC anyway. If your PC ran Windows 8 without issue, it will definitely be OK for 10.
• 1 gigahertz (GHz) or faster
• RAM: 1 gigabyte (GB) (32-bit) or 2 GB (64-bit)
• Free hard disk space: 16 GB • Graphics card: Microsoft DirectX 9 graphics device with WDDM driver
•A Microsoft account and Internet access
How to uprade to Windows 10 if you're on Windows 7 or Windows 8
Starting today, people who reserved their upgrade to Windows 10 will be notified in waves. If you haven't yet reserved your upgrade, make sure your machine is up-to-date through Windows Update first of all.
You need the KB3035583 update specifically - that's the one that dumps a small Windows logo next to your notification area (on the bottom right of your taskbar). This looks like the example in our main image above.
Clicking this takes you to the Windows 10 Update App. In the app, you can 'reserve' a copy of the Windows 10 update for free. When it's available, you'll be notified and you can start the download. Your existing Windows licence will transfer to a Windows 10 one.
If you haven't yet requested it, it will take a few days for your update to become available, simply because there are so many people downloading Windows 10 from Microsoft at the moment.
If you want to clean install Windows 10 on Windows 7, 8 or 8.1, then download a Windows 10 ISO. You must run the ISO on your existing Windows 7, 8 or 8.1 install to get the free upgrade. This is called an 'in place' upgrade.
What to do if you're on Windows XP or Windows Vista
You'll need to do a clean install. One way to do this is to download the Windows 10 ISO (basically the installation file) to create your own installation USB stick. This is a relatively simple process BUT because you're not upgrading from an existing Windows 7, 8 or 8.1 install you won't get a free upgrade and you will need to buy a license.
You can also buy the Windows 10 software from Amazon starting at £99.
A cheaper way: One clever fix is to buy Windows 7 and upgrade to 10 that way (although you will also have to download and install a helluva lot of Windows Updates first). Some places online are selling Windows 7 for not a lot, so shop around.
What Windows 10 version will I get?
You'll get the equivalent version to what you're upgrading from. So if you're going from Windows 7 Home, you'll get Windows 10 home and so on.
Volume licence holders can get Windows 10 Enterprise and Windows 10 Educaton starting on 1 August.
Here's all our other great Windows 10 coverage so far: