Log in to your facebook account and go to your facebook admin page. It should look like this:
Make sure you are posting as your page, not your personal account. Look in the right hand corner, if you see your personal account name, go to the Edit Page Drop Down and click Use Facebook as:
To find and older post use this short cut:
Click on the right hand corner of the post you would like to remove. Select Delete from the drop down menu.
Refresh your page and the post will be deleted.