Welcome to the forum!
There is a thread somewhere here that shows pictures of how to remove the panel in the centre. Starts by levering the little tray out of the top, remove the screws, then repeat at the bottom (I think).
Don't worry about wiring. There's a harness inside that the head unit plugs into. You can buy an adapter if that doesn't fit your new head unit - here in Australia, they're available in most places that sell car stereos. Get one and it's just plug and play!