ASDF is an incredible version manager, to install/upgrade to latest version available of an language you can do the following steps:
asdf list-all <language>
this show all of the versions available to install, select the latest:
asdf install <language> x.y.z
and edit if you have a global ~/.tool-versions
to use that version everywhere:
<languaje> x.y.z
real example
to upgrade to latest version of erlang (10/17/2019):
asdf list-all erlang
asdf install erlang 22.1
asdf global erlang 22.1