I don't know if you can still upgrade for free. But you can try.
NOTE: A clean install will wipe out your C: drive. You might want to try an upgrade install first.
DO YOU HAVE A BACKUP OF YOUR FILES? Installed programs cannot be backed up, you must reinstall if you do a clean install.
Download the Windows 10 ISO and create a USB drive.
go here > https://www.microsoft.com/en-us/software-download/windows10
Boot from the USB and follow directions to install the equivalent version as your W7.
When connected to the internet, if you can activate it, then you are good to go.