Follow the instructions in this thread
to have your stories removed. You will have to repeat the same procedure for each piece, but it shouldn't take long if you open a list of your work in another tab or window first.
As for deleting your account, you can edit the posts you don't want to five characters (like periods), and once you're done with everything on this site, log out, clear your cookies and walk away. No admin intervention is necessary unless you have an extremely compelling reason to have the account modified.