The documentation of
package-install says: "Install the package PKG. PKG can be [...] a symbol naming one of the available packages in an archive in ‘package-archives’."
To install the latest version of Aggressive Indent Mode, I have tried:
(package-install 'aggressive-indent-1.8.3) (package-install 'aggressive-indent-1.8.3.el)
But both of them make Emacs drop into the Lisp debugger. I cannot use simply:
which would work, because I already have an older version of Aggressive Indent Mode installed.