I don't think 2.14 has been officially released yet. The way the naming scheme works in GitHub is that pre-releases are given a branch, previous releases are given a tag, and the master branch represents the current release.
Once 2.14 becomes official, it will be merged into master and you can simply do a git pull of the master branch to update the code. You will probably have to update the database afterward.
If you want to go to 2.14 now, then the right thing to do is check out the rel-ww2.14 branch. I've been using it here for the last term without any problems. Unfortunately I don't see the release notes in the wiki. If memory serves, the only things required were updating the code and the database, but it's possible I had to do more and just don't remember.