libraries: install or update?

when updates for libraries are available, after selection of the latest version there are two buttons, "install" and "update".

What is the difference between both and what is the best way?
(I usually klick on "install")


The "Install" button installs the library version selected in the dropdown menu to its left.

The "Update" button installs the newest version of the library available.

If you have the newest version of the library selected from the dropdown menu then "Install" and "Update" do the same thing.

OK, thank you