If you look at the upper right hand side of your post you'll find a button named "EDIT ///".

So, this site has an option to edit your posts.

However, you cannot delete it. This will ensure -among other issues- data integrity, since it's possible to be referenced by a different post.

In case of special circumstances site owners might delete a post - but not without contacting the OP, I believe.

Edit: rephrased.