i need a help,thank you very much.

You can not edit posts. All you can do is try to be very careful the first time. I know kitty mentioned starting a new discussion to fix the mistakes or clarify but really, double posts like that can get annoying. It's better to just let it go and clarify in a comment when people respond to the discussion. If it is a response that you made a mistake in, instead of making a whole new response, just add a comment after it explaining your mistake.

I think you can not really edit your discussions, but you can start a new one to statement which part you want to change or edit! I am also quite new here! : ( sorry can not give you more suggestion! maybe someone else will give you useful comments! And I also want to know about that! : )