Is it true that you can upgrade from Windows 7 to Windows 10 for free?
If so, how can you upgrade from windows 7 to windows 10?
Yes. Microsoft will make a download available which will update your installation to windows 10.
Note: this free upgrade will not remain free forever. Only for a limited time of 1 year, up until the 29th of July 2016.
After this, you can reinstall Windows 10, but only on a modern machine which uses UEFI (as the key will be embedded); however if you reset your BIOS or change the motherboard, you will need to purchase a Windows 10 licence in order to reactivate.