So, Can I upgrade from "Pirated" Windows 7 to Legal free windows 10 using the upgrade tool on MS site?
You must understand one important thing, Windows 10 has never been free, if you didn't have a legitimate Windows 7 or Windows 8 license when you first installed Windows 10 then you have always had a pirated copy of Windows 10.
I had to install Windows 7 on my machine for some reason and now I want to get back to Windows 10. Unfortunately, I don't have windows 7 license the one I'm using is pirated. And the new windows 10, I want to use unactivated free version instead.
Just download the Media Creation Tool and from within Windows launch the Setup.exe after you create the installation media. Windows 7 doesn't have to be activated in order to upgrade to Windows 10.
Can I do the upgrade without any USB or removable media?
In order to upgrade to Windows 10 you need a working Windows 10 installation media. You can run the Setup.exe from within Windows 7, however, due to the fact Windows 7 does NOT have the ability to mount ISO natively you will be unable to avoid the creation of an installation media.
Has been pointed out in numerous answers to existing questions about the activation of Windows 10, Windows 10 uses a digital entitlement system, so your Windows 10 will likely automatically activate once you install it. I will point out that there is no actual free version of Windows 10, in order to activate your installation, you must have a legitimate Windows license.