First, update your homebrew formulae:
>brew update
Updated Homebrew from 98dc2cdb to 5dff180c.
[omitted]
Second, check what is outdated:
>brew outdated
cmake (2.8.12.2 3.0.0)
Finally, update all outdated packages with
brew upgrade
or certain packages with
brew upgrade $FORMULA
Depending on the packages, this step may take a while.
From time to time you might want to delete old packages:
#check what will be removed
brew cleanup -n
#remove all
brew cleanup
#remove certain packages
brew cleanup $FORMULA
More information about homebrew usage can be found in the homebrew wiki.