homebrew update git on mac

homebrew update git on mac

i'm trying to switch to homebrew's version of git but i get the following
message:
unknown68a86d401752:~ davidadams$ brew link git
Linking /usr/local/Cellar/git/1.8.4... Warning: Could not link git.
Unlinking...
Error: Could not symlink file:
/usr/local/Cellar/git/1.8.4/share/zsh/site-functions/git-completion.bash
Target /usr/local/share/zsh/site-functions/git-completion.bash already
exists. You may need to delete it.
To force the link and overwrite all other conflicting files, do:
brew link --overwrite formula_name
To list all files that would be deleted:
brew link --overwrite --dry-run formula_name
I don't know enough about Homebrew or bins to know if what this is
suggesting is safe to do.
My goal is to start using a current version of git. Terminal tells me the
following:
unknown68a86d401752:~ davidadams$ which git
/usr/bin/git
unknown68a86d401752:~ davidadams$ git --version
git version 1.7.7.5 (Apple Git-26)