If orphaned, the Forum Team (VM employees) will be able to help. If linked to your account as a secondary address, you should be able to delete it yourself in the billing account, manage accounts tab.
If the primary address, it can't be deleted, but if you review all the settings in webmail, and delete all the contents - emails and contacts. Delete it from any email client and ignore it for 150 days it is supposed to go dormant.
I hope this helps, let us know if you require assistance.