I’m trying to change the version, but it doesn’t work
Hey @Hankatt0815!
Firstly, you can’t downgrade the engine version of your project.
If you’re trying to upgrade though, make sure that the engine version you’re trying to switch to is installed.
Hope this helps! 
You can technically downgrade, but you need to set the correct build order for it to work. Sometimes you also need to filddle around with the compiler and sdk if you need to jump many versions.
The source files will compile but the uassets made in higher versions will be broken.