New
#31
The TP currently has an expiration date of April 15. With the January 21 release of the TP, there could well be a new expiration date. We just don't know at this point.
In the past, no matter which product was being tested, the Beta, TP, whatever it's called, must be uninstalled before installing the final product, sometimes called RTM (Release to Market). One thing to note is that Microsoft is getting better and better at this; it may well be that we'll be able to just upgrade, but don't count on anything to be written in stone.
However, if it were me, I would not replace my Windows 7 or 8.1 OS with Windows 10 at this point. As Jeff said, you can always install on a VM (virtual machine).