Following the instructions detailled here: http://www.smashingmagazine.com/2014/05/19/moving-git-repository-new-server/
Here are the steps eventually run:
git fetch origin
git remote add new-origin ssh://john.smith@192.168.2.3/volume1/git-server/is.git
git pull new-origin master
git push --all new-origin
git push --tags new-origin
git remote rm origin
git remote rename new-origin origin