if its activated now, it will be activated after the install. Microsoft were sort of lenient when it came to upgrading people to win 10, they much prefer people on it than scattered over multiple versions of windows, its easier to upgrade everyone then.
look in settings/update & security/activation
if it says Windows is activated with a digital license, then the license is still tied to your hardware.
If it says Windows is activated with a digital license linked to your Microsoft account then the licence is linked to your Microsoft account, if you set up user using same Name & email address and password, it is likely to reactivate once it is installed.
When installing win 10 and you get to screen asking for key, click the "I don't have a key" button and install will continue and reactivate once install finished. Keys stored on Microsoft activation servers, PC will check it is okay to reactivate by checking one of these servers.