Fitting a CD Changer

I have just bought a Sony CDX-T69 CD Changer for my 52 plate Punto. I'd like to have a go at fitting it myself, bit I have a huge problem, I don't even know where to start.
I was hoping to put the changer in my glove box but it won't fit, so was thinking placing it under the passenger seat. If I do this where do I connect the chager too? Do I need to take my current cassete player out to get to the back?
Sorry I am pretty clueless but any help will be much appreciated.

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