$ git fetch downloads the latest from remote without trying to merge or rebase anything. Then the $git reset resets the master branch to what you just fetched.
[www@hostname current]$ git fetch --all
Fetching origin
From github.com:iceskysl/www
ad05fc..2009e v3 -> origin/v3
[www@hostname current]$ git reset --hard origin/v3
HEAD is now at 205809e Merge pull request #42 from IceskYsl/v3