I got a copy reserved for my laptop, will upgrade from 8.1, but will not be upgrading my Windows 7 or 8.1 on my desktop, I'll be triple booting. Just don't know if I can upgrade my build to the RTM. Have to wait and see I guess.
Head of Windows Insiders Gabriel Aul has confirmed on Twitter that all members in the program using the Windows 10 Technical Preview (or the Insider Preview as it is now called) will be able to upgrade to the RTM build of Windows 10 for free.
Officially MS won't permit you to upgrade from this TP to the RTM.
"But as with previous versions there is a workaround where you change the build number to something else which tricks the installer into upgrading for you"
"There's also the issue that there's no retail equivalent of a Tech Preview anyway as Pro, Enterprise, etc. SKUs don't exactly correspond to it. Ergo, there's no way to reliably update from the TP to a retail SKU without potentially breaking stuff, e.g. what if you were using Enterprise feature but could only upgrade to Pro?"
Since it is only a TP, should be a fast reinstall for the RTM. I'd start fresh. After making a full image backup to fall back to in case of any crisis.