Now that the end of Win7 support is nigh, I've done lots of upgrades to Win10. The option has been a public secret among service shops and it has been mentioned in some PC magazines as well.
There's several ways to do it:
1) Download the Tool from
https://www.microsoft.com/en-us/software-download/windows10, change the en-us to your locale if needed. Start the Tool and choose "Upgrade this computer now". That will leave all your programs and files intact, including any garbage, so uninstall any obsolete programs including your anti-virus and get rid of all junk files.
2) Start the Tool as above but create an installing media (read: >8 Gb memory stick) to be used on your computer. Boot from that stick.
3) As above but uncheck the "For this computer" option so you can use it on any computer. When the installation asks for the code, use the Windows 7 code on the sticker of your computer.
4) Options 1 and possibly 2 include an option to undo the upgrade within 10 days. However, having once installed and activated 10 on that computer will leave the electronic activation valid so you can do a clean install Win10 on that machine without any code and even on a fresh new hard disk in the future!
Thus, if your computer is still up to the task but you're uncertain about getting 10 right now, choose option 1 and revert back to Win7 after having checked that Win 10 has been successfully activated.
