How to upgrade Homebrew itself (not softwares/formulas installed by it) on macOS 10.12.3? I have homebrew installed long before the OS is upgraded a few times to 10.12.3. Now that 

$ brew --version
Homebrew 0.9.9 (git revision 080c; last commit 2016-08-11)
Homebrew/homebrew-core (git revision b163b; last commit 2016-08-10)


How to properly upgrade to newer version, say 1.1?

$ brew upgrade 


didn't work.
To update homebrew itself, use:
brew update

To upgrade all packages installed using homebrew, then you have to use brew upgrade. You can check this FAQ from brew website for more details.