Im on mac OSX, so I go to terminal CLI and do

brew install ethereum


then I get

==> Downloading https://build.ethdev.com/builds/OSX%20Go%20master%20brew/193/bottle/ethereum-1.1.0.yosemite.bottle.193.tar.gz
######################################################################## 100.0%
==> Pouring ethereum-1.1.0.yosemite.bottle.193.tar.gz


So now I'm left with Ethereum 1.1 , but I need 1.3.1 how do I fix this?

First run

brew update


To update the "formulae" (this is the brew-specific word for "catalogue") of all the open source projects it knows.

Then run

brew upgrade ethereum


(Sometimes you'll need to uninstall and reinstall the formula to make it fully work).

With

brew info ethereum


You can check what you have installed now.