If it is a post you made within the past 48 hours, you should be able to edit the post and remove the attachment yourself.
Beyond this time, you'll need to ask the moderation team to remove it for you. The easiest way to do this is to report the post in question and provide a brief explanation of what you would like done and why. This will alert the moderators who can take care of it.
PS. I've already remove the attachment in question for you as a result of your email.