Spark comes out with a new version roughly every couple of weeks. You might be inclined to just download the latest update every time a new one comes out, but it can be a risk. Spark is great but it is not without quirks. I’ve heard stories of creators working on a project and finding a bug that makes the project unrecoverable and all of their work is lost. There is no going back to a previous version once you upgrade your project!!
So in the spirit of not losing hours/days/weeks of work to a bug in the program, I’ll share my workflow for managing Spark versions.
First of all, it’s good to know where the downloads page is. If you need an older version of spark, you can grab it from the downloads page: https://sparkar.facebook.com/ar-studio/learn/downloads/
In practice, I usually lean on the auto updater, but it overwrites the current version of Spark. Before I run the updater, I make a copy of the app and rename it with the corresponding version number. After I have a copy of the current version, I run the updater on the main app. My app folder ends up looking like this:
As far as deciding what version to use for a project, I recommend NOT using the latest version. Instead, I work with a version that I know is stable and has the minimum feature set that I need. This saves me from discovering new bugs in the middle of a client project 
It can be hard to keep track of which app version your project is using, especially after coming back to it after weeks or months. My convention for this is to add an empty version file just so I can see which app version I should use to open the project. It’s a small detail but it saves me the frustration of opening the wrong version, closing, reopening. Time is money, damnit!
@Tomas_Pietravallo told me that his app was automatically installing updates, but I couldn’t find anything that did that in the preferences. It turns out there’s a checkbox on the upgrade dialog box, toward the bottom. To open this dialog, you can go to file > check for updates (on any version that isn’t the latest).
) - downgrading after I finish this project