SHELL

rename heroku app

$ heroku apps:rename newname
Renaming oldname to newname... done
http://newname.herokuapp.com/ | git@herokuapp.com:newname.git
Git remote heroku updated

heroku rename

heroku apps:remane --app <old-project-name> <new-project-name>

heroku rename app

heroku apps:rename new_name --app old_name

rename heroku app local

First update the name for the heroku app on the heroku dashboard (on the heroku website)
Then do this on terminal (Make sure you're in the right repository)

$ git remote rm heroku (Remove the remote from git)
$ heroku git:remote -a <new app name> (Add it back with it's new name)

renaming heroku app

$ git remote rm heroku
$ heroku git:remote -a newname