well. Don't get too excited about your set up.
You have not upgraded Ubuntu-shipped elixir this way. The proper way of doing it would be by installing a DEB package.
You have installed elixir the manual way. Which means it's installed without any dependencies and thanks to $PATH priority you are using newer version of Elixir. But the old one is also in the system.
I do not think this is proper set up and if you install packages this way, you will have trouble in the long run.
You can install packages provided by Erlang Solutions as instructions show here: https://www.erlang-solutions.com/resources/download.html
These are for both: Elixir and Erlang. Uninstall the system-provided versions, add those repositories and install what you need. They will update nicely.
Having said that, they don't have ELixir 1.4 released just yet. It will take them a few days at least to do so I think.
You also have the option to use version manager, that is independent from system packages. I use
The version manager allows you to have multiple versions of Erlang, Ruby, Node or Elixir installed at the same time and switch between those on per-project basis. Very useful if you run more than one project. I highly recommend you going this route.