How to clean CI/CD history logs and builds?

I want to delete my old pipelines. How can I do that?
I know there is currently no option available via the UI, but is there a manual way to do that for a specific repo?

I have the newest Gitlab CE installed.

did you find anyway to clean old builds?
is there a new feature for that?

Hey @jan561 and @rvalle, as of GitLab 11.6 you can delete pipelines via the API.