Welcome back Joe 
As @cpgo mentioned, it’s often beneficial to have multiple versions of languages installed as some projects may depend on different versions. For this we use an Elixir version manager (like ASDF).
As mention by @NobbZ, Mix is installed with Elixir.
If you use a language version manager then you may find you don’t need to uninstall older versions, but if you do the method will depend on which version manager you use.
I would recommend most people use a language version manager because you may need to work on older projects that are tied to older versions of languages. They are also used in production - so a server can host different apps using different versions of languages or frameworks. Some LVMs can even compartmentalise packages (such as Gems if you’re using a language such as Ruby) so that they are only loaded for that specific app/version (so are therefore more efficient/performant for the server).
Have a look here to see some of the version managers available for Elixir:
If you have any other questions or you’d rather not use a LVM, let us know how you have installed previous versions and we can help with how to remove them.
