Hi Christiane Buttke
You don't need a license for MultiTerm if you have bought Studio so don't worry about that.
Your account should show what you have bought accurately so I think probably you bought an upgrade from 2015 to 2017 which was then upgraded to 2019.
If you have installed Studio 2019, you should not need the previous versions but when you upgrade to a new version, the previous version is still usable on your machine, so long as you don't uninstall it.
MultiTerm comes free with a purchase of Studio so it sounds as if you just haven't downloaded and installed it.
You can download the latest versions from your SDL account, here:
My SDL account
Click on Downloads then scroll down to the following two entries:
Ignore the 'Widget' download unless you want to run Widget as part of a business network setup.
You can install Studio 2019 SR1 over the top of your existing Studio installation, if you haven't already.
The only version of MultiTerm that is compatible with Studio 2019 SR1 is MultiTerm 2019 CU1 as you see above.
I hope this helps!
All the best