replacing the casette player in a Nubira CDX 1999?

Hi Im just in process of picking up a rather nice 1999 daewoo Nubira 2.0 CDX, but is has a casette player. I bought the well recomended Argos Alba In car Cd/Radio ICS 103, ready to fit in, when I pick up the car next week.

Do you think its worth downoading the manual for this car, as it would seem, this vehicle may have 6 speakers, although Im A past Motor mechanic in the Eighties, with some car electrical experiance, Im not sure these days how to replace the Alba's normal 4 speaker leads and ISO conections into the wiring of a 6 speaker one.

I take it, I should test which Speakers that maybe just tweeters? and remove those connections, seal there ends and use the cars main 4 speakers and connect them to the Alba's 4 outputs.

Any help grateful.

Thanks