upgrade from express 6 to 7

That's easy.

Just download Prime7 and install. Don't (try to) enter a license. That's it, you have Prime 7 express.

If you want to make use of the trial period to experience the full feature set, you do need to get a license. This will expire after 30 days and from then on it functions as Prime 7 express.

Note that you do not need to uninstall Prime 6. You can run all prime versions side by side (The only exception is Prime 3 and 3.1), but you have to install them in the order of releases.

For more information on dowloading and installation see here.

Success!
Luc

Mathcad Prime 7.0:

https://www.mathcad.com/en/try-and-buy/mathcad-express-free-download/install

https://free-dl.ptc.com/install/pim_installmgr_mathcad.exe