As of git 1.7.0, you can do this way
$ git push <remote> --delete <branchname>
In earlier versions (git > 1.5.0) you have to do
$ git push <remote> :<branchname>
To remove a branch in Github, in remote use origin.
did you want to say git < 1.5.0 ?
@ashutoshraina no, what I said is right, this action was included since version 1.5.0 look here https://github.com/gitster/git/blob/master/Documentation/RelNotes/1.5.0.txt#L172-L174