@browj2 is perfectly correct but, just to be absolutely sure that you have a fallback if needed, I would strongly suggest creating a copy of your project file and open this copy in the new version to work on.
IOW, should the worst happen and the project file "fail" you will still have the "original" version to return to.
Sorry for not writing more, but I had to go out and I wanted to give you a reply.
You may find that the 2020 program overwrites 2019. I have 2019 and a much older version, so I don't really know. Your projects are safe as they are in your Documents.... not with the project files. Just make sure to back up project files and source files, video, photos, audio, to somewhere safe, like the cloud. You may also have to download and install the additional content again.
Just so that you know, PhotoStory project files can be opened with Movie Edit Pro Plus/Premium and Video Pro X (which is what I use), in case you ever wanted to get something with a bit better editing tools. Your projects will not be lost.
As well, old project file can be opened in newer versions of the program, but not the inverse, usually. However, sometimes certain templates and audio, get removed from a newer version, or they are moved and can't be found. This is rare, but can happen. Magix seems to have fixed this as the previous version templates are now kept in a Public folder, not ProgramData, and do not get overwritten (I hope).
Thanks so much for all help - I feel reassured and have ordered Photo
story 2020. Also interesting to hear projects can be open in Movie Edit too.
Just consider that after updating, you may have a 8hr blackout... because you will be asked to download 4gb of additional content. Without them, you may not be able to edit your project (depending on the elements you used)
The time to download the additional data don't depend that much on your internet speed, but rather on Magix Servers, that (as you can see on several posts here) suffer from speed problems