When using git branches and pushing them to a remote you inevitably need to do some tidy up.

Deleting a local branch:

git branch -d branch_to_delete

Deleting a local branch that is not in the current history:

git branch -D branch_to_delete

Deleting a branch in the remote (origin) repo:

git push origin :branch_to_delete

Deleting the local copy of a remote branch:

git branch -d -r origin/branch_to_delete

Cleaning up your local copies of remote branches (matching the branches on the remote):

git fetch -p

(Source: wiki.sourcemage.org)