I've purchased and installed the 2017 version. A few months ago I also purchased the 2019 premium version on sale but have not yet installed it. Will installing 2019 on the same Windows 10 PC wipe out my 2017 files, or will content be preserved? Thanks.
Music Maker 2019 will replace 2017, however all Instruments and features should be preserved, additionally you should download and install all your purchased content again as it much of it has been updated.
Soundpools should also be preserved, however if you have any from a much older version of MMM they may not be available.
There is only 1 version of the MusicMaker engine and it's free. The current version is 2020 and it is free.
When you purchase a new version, like 2019 Premium, you are purchasing some Features, Presets, Instruments and Soundpools. For most of these, you will receive coupon credits that show up at the bottom of the relevant screen under the Store. You are not purchasing a new version of the program.
If you "buy" the 2020 Premium version, you will just receive more credits, not the program itself which is free.
You should update to the 2020 version first. Then activate your 2019 Premium code. Then, making sure that you are logged into the Store, click on the Download button at the top right and download AND install everything that is listed. Once you've done that, you can start spending the credits on stuff that you don't have. Use the credits carefully.
Watch this tutorial for more. The new version (2020) is slightly different.