Click the 'My Posts' link on the right hand sidebar. You'll see a list of your posts, with edit and delete links on the right side of the list.
Click edit, and you'll be taken to the form you used to post your event. From here you can edit your post - add details, correct spelling errors, whatever you need to do. When you're done, click submit at the bottom of the form to save your work.
Click delete, and the system will ask you if you're sure you want to delete your post. Click the delete button to confirm.