Click on the Lists link in the Mail Menu area.
Click on the 
next to the mailing list that you want to delete.
Delete a Mailman mailing list when you no longer want the list to be active.
Warning: Deleting the mailing list will delete all archives, current mail, and members email addresses. If you want to keep any of this information, be sure to download or otherwise copy these files before deleting the mailing list. Once the mailing list is deleted the information is unrecoverable.
To delete a mailing list:
Click on the Lists link in the Mail Menu area.
Click on the next to the mailing list that you want to delete.