You can't. But if you /msg the gods (look for the Chatterbox Nodelet and the "Talk" button) you may be able to have the account disabled or renamed.
The OP may also /msg the gods using the Message Outbox, or via the link on the gods usergroup page. :-)
Today I remembered that I used to post here. I connected and saw that my account was still here. I was more amazed that I remembered my password.
When I saw your post requesting to remove a old account, I thought once a monk always a monk.
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