Originally Posted by Wikidbchofthewst

If the post is recent there should be an edit button down by the "quote", "multi", and "quick" buttons at the bottom right corner of your post. You just view it in the thread and click it. If you still can't find it I circled it in red in the thumbnail

As for deactivating your account, you can't. If there's some special reason, you could always PM a mod about it, and see if they can help you out. But there's no way for you to delete your account on your own.