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.
Bought a souvenir
Emailed all my friends about it
Got blowed up
Hit him right dead in the jaw
Made it awkward
Took a selfie
Want to go home
Results (348 votes). Check out past polls.