If you have a PC with Windows 7 or Windows 8 installed and you have it activated with an original license, you can upgrade to Windows 10 for free.
To date, Microsoft still allows you to upgrade to Windows 10 if the above described case occurs. We only have to visit their official website: https://www.microsoft.com/es-es/software-download/windows10
We'll download the tool you offer and give you "Update this computer now"
It will download Windows 10 and install itself.
There will be a time when we will be asked if we want to keep our personal files and applications. We'll say yes and click "Next".
Once the installation process is complete, we will have managed to get hold of Windows 10 for free.