Switching between releases of solutions in Version 3.5

[Lagoona]

I have recently taken over managing Servoy for a company and am fairly new to it. They are still using Version 3.5.1-build 514.
My long term goal is to upgrade to version 5 but it is a large complex system and I'm reluctant to move until I'm much more familiar with it.
For now I have a question (no doubt more in the future) about the current version that I would like to clear up -
I have created a new release of a solution so that I can work on it while the users use the currently active one. However, I then wanted to make a small change to the release they are using and I find that you can only save changes to the newest release - this makes it very awkward to use as I would keep having to switch the active solution if they ask for minor changes. But maybe this is not so bad - do I have to shut down all clients and maybe flush the solution or restart Servoy when changing the curently used release of a solution? Is it easy to switch between releases? I want to make sure I get this right as a lot of people depend on the solutions working correctly.
Also could anyone point me to any articles/tutorials on how to upgrade from this current Version 3.5.1-build 514 of Servoy to the latest version 5.

Many thanks