HEAD UNIT - How do I fit an aftermarket one??? What adapters are needed etc???

Hello,

How do I fit an aftermarket head unit.... What adapters do I need?

I have the 6 disc cabbasse auditorium in at the moment.

Its been broken for a year, I have no idea how to fix it and dont have a clue how to fit a new CD player.

Any help would be appreciated!

Thank