new head unit

I have been given some vouchers to use at halfords, only thing i can think of is a new head unit that i can plug my ipod into.

Car is a GLX Octavia, question is to change the head unit what do i have to do, or be aware of?

I have got some bent metal clothes hangers so getting the old unit out isn't an issue. On the back are a few connectors, ariel, power? are these standard fittings?

In the dash is a metal frame into which the headunit fits, is this specific to the head unit? and to remove is it simply pull, with a bit of help from a screwdriver?

Thanks