This is how to upgrade the installed version of jrnl. You can see the version that is installed by:

jrnl -v

Check at pip - jrnl to see what the latest version is and compare it to what you have installed. If what is available is later (i.e. great number), then you could upgrade it.

Since I installed it with brew, the way to do that is:

brew upgrade jrnl

That seemed to work.