How do I delete a remote bookmark in Mercurial?

With hg-git it is not possible at the moment.

You have to install the git client, clone the repo and issue a

git push origin :oldbranch

to delete the old branch. Hopefully there will be a patch one day.

To delete a bookmark from a remote server, you must have permission to push to the server. If you can push to it, then you can:

hg bookmark --delete <bookmark name>
hg push --bookmark <bookmark name>

See the "Working With Remote Repositories" section of the Mercurial BookmarksExtension wiki for further info.

NOTE: This only removes the bookmark itself. It does not remove any changesets that were associated with the bookmark. If you need to remove the changesets themselves, then you must consider other methods as noted in these related questions.