[answered]I need your help

You can't delete all your posts. You could edit them all but when a moderator notices what you are doing your account would just be banned preventing further edits.

For whatever reasons many people decide they want certain posts or their whole posting history removed.

With very rare exceptions it does not work that way here. If you think it's one of the rare exceptions you should contact the moderator account (look at teh first page of the member list).

Re: [answered]I need your help
Thank you. I hope they will understand me and they will delete all my posts.