Unless you are maintaining a multi-user machine, just download and extract the tarball it wherever you like (eg I generally keep them in various directories like ~/src/julia-1.2), put it in the environment variable PATH, and you are done.
Some Linux users like to have a single directory for various scripts, eg ~/bin, and put that in PATH. In that case, just make a symlink to the Julia binary from there.
Generally it makes sense to keep multiple Julia binaries around, eg for testing on an earlier version, or trying out a pre-release, just name symlinks accordingly.
These may help:
https://askubuntu.com/questions/141718/what-is-the-path-environment-variable-and-how-do-i-add-to-it
https://askubuntu.com/questions/324930/question-about-the-symlink-of-the-ln-command