The only way to delete your posts is to delete them yourself manually. And it's an old school forum, you cannot actually entirely remove them, just empty the contents of the posts.
Just click on "Quick Edit" and replace your post with a row of dots or something, and then move on to the next post.
I'd suggest to get to it (if you truly want this), you only have 182 posts so far, that's quite manageable to delete, but it will still take time.