Speaker sizes??

Hey everyone...I just had some questions.
My brother has a 93 850GLT and most of his speakers have blown so I want to get him new ones. I know that there are eight speakers in the car but what I'd like some help with is this: What sizes are they and can I just buy new ones from an audio shop without re-wiring the whole car?
Any help on this would be greatly appreciated.
Thanks

if u just want speakers im pretty sure u just put them in.. unless u want a whole system, with a woofer and an amp and everything. then u gotta run some cables