You can edit a post before you publish it, or afterwards.
Before you publish
Return to a post you have previously saved, and click Edit to open it.
You can change all aspects of the post: title, text, post type, signature, tags and services.
Don't forget to save your changes.
When you are ready, publish your post for everyone to read.
After you publish
It is considered "bad form" to make significant changes to a post after it is published, unless you make clear where the changes are.
For example, you might want to add new information. You could make the change obvious by writing "UPDATE 12/ Dec 2013: new information...."
The reason for this is that some people may already have responded to your original text.
Of course, you can always make minor corrections to spelling etc. without upsetting anyone.
Deleting a post
You can delete any of your posts before they are published.
Once a post is published, you must unpublish before you can delete.
Again, unpublishing or deleting a post to which people have already responded would be regarded as impolite.