Click the 'edit' button in the lower left portion of the post you wish to edit:
You can change the title and the text once you are in the edit screen.
Edit: Whoops. Look like you figured it out whilst I was typing.
If you want a post to be locked/deleted, just change the title to 'please lock', or 'please delete' and a mod can take care of it (lock for sure, not sure if all mods can delete).