git remote url git for currently existing present folder
git remote set-url origin git://new.location
(alternatively, open .git/config, look for [remote "origin"], and edit the url = line.
You can check it worked by examining the remotes:
git remote -v
# origin git://new.location (fetch)
# origin git://new.location (push)
Next time you push, you'll have to specify the new upstream branch, e.g.:
git push -u origin master