Assuming the DVD player is built in then you should only have a power feed. You should see the cables underneath the seat base and then trace them to where they are connected. They should be fused into at least an ignition live in one of the fuse boxes. You might be lucky if there is a suitable connection under one of the seats if not it will be in the dash. Once disconnected you should be able to pul the cables through to the headrest unless its been cable tied in to existing looms. If there is any securing behind the seat covers look on you tube there should be plenty of videos on how to remove the seat covers