Well, first of all, you've posted this on the Mathcad Installation board. I'll see if this can get moved to here: https://community.ptc.com/t5/System-Administration/bd-p/cesystemadministration
Anyway, go to https://support.ptc.com/appserver/auth/it/esd/product.jsp?prodFamily=CML and log in to your PTC Account.
If you're entitled to Creo Elements/Direct Modeling (as in, you actually have a software licence for it because you/your organisation bought it), you should see the page populated with stuff.
You'll find 20.3.4.0 under Release 20.3 and then under "Show all Other Available Versions".
Step 2: Click the HTTP download now button on the "Creo-Elements-Direct-Modeling-20-3-4-0-64bit (1684 MB)" file. (Maybe you want the other files, too, I don't actually know much about Creo Elements/Direct.) It's a big .exe.
There will be further instructions on the installer once it has downloaded, but I'm not going to download it myself, so that's as far as I can help you.
