Simple and pretty neat trick:
Lets say your project repository in my
$HOME/dev/SampleProject
directory.cd $HOME/dev/SampleProject
git remote rename origin bitbucket git remote add origin https://github.com/sample/SampleProject
.git git push origin master
git remote rm bitbucket
It'll only remove your local reference not your origin repository.
Tags:
You'll notice that your tags are still not visible in github. You may need to run single command on terminal:
git push origin --tags -f