Officially, the free upgrade offer ended on 07/29/16. However, the original upgrade process still works unofficially for most folks. Microsoft doesn't talk about it at all and will not refer to it under any circumstances (probably due to their OEM contracts), but they haven't removed the media tool used for the upgrade process either.
The best way I've found to do it is to
download the media creation tool and use the "create a USB drive" option when attempting to install on a questionable machine. You will need the Windows product code on the paper tag on the laptop, not the one that was used to install Windows (that is an OEM dummy code that won't work for a Win10 install). By using the USB drive, you can easily make multiple attempts. Make sure the machine is hooked up to the Internet when you run the upgrade as it will download updates during the process.
I just upgraded a 9 year old Dell E4310 laptop about two weeks ago and it worked fine (other than missing a few drivers - the Win7 drivers on the Dell webpage worked just fine after the fact). Do make sure you have the most recent BIOS upgrade installed before upgrading, and make sure that all your Win7 drivers are up to date (especially for oddball devices like card readers or fingerprint readers). The Win10 installer is pretty intelligent and will stop the upgrade process if it finds incompatible hardware. If this happens to you, look up the hardware ID in device manager and try to find a more recent Win7 driver for the hardware at issue -- afterwards, it will often work on the next try.
