If you don't want to use homebrew on mac, here is the list of commands I used to upgrade: https://gist.github.com/jazzychad/07c0c6da5709202e8106
Also, your github profile picture is amazing.
ls -al /usr/bin/git
If it's not in fact a symlink then yes you should probably rename it to preserve it.sudo mv /usr/bin/git /usr/bin/git2
before the symlink.