Easily the most-requested feature on openmikes.org -- "how can I edit my listings?" Short answer until now: you can't. Leave a comment, and I edit them.
New longer answer -- if it's really yours, and you're logged in, you can edit parts of the listing. See the help page on editing for details.
You can't delete comments, yet -- you'll eventually be able to delete your own, but you'll never be allowed to delete others'. And you can't yet change, say, a weekly open mike to monthly, etc. -- that's still on the drop-me-a-line list.
Feedback is welcome, as ever.