When I’m giving an existing Facebook page a tune-up or setting up an ad campaign for my clients, they need to know how to add me as an admin to their page (directions at the Facebook Help Center, above). I request to be added as a Content Creator. That means I can edit the page, moderate comments, view insights, and create ads – but I can’t remove the original admin (manager) from the page and take over ownership of it. Note: the person has to ‘like’ your page in order to show up on the list of potential admins in step 3.
How To Add An Admin To Your Facebook Page
Step by step instructions at the help center at facebook.com