If you want to remove a post from the content library, you can do that by archiving it. To archive a post, navigate to the 'Posts' section of your manager view and find the post you would like to archive. Once you've found the post you'd like to archive, click on the settings button for that post.
Next, select 'Archive' from the drop down menu.
You can then find the archived post in the 'Archived' tab of the posts section.