Unfortunately it's neither simple or cheap. Unlike the current Nissan/Infiniti vehicles where everything's pretty much built into the head unit, on 2008-2012 EX35 models the radio and gps are separate components. Frankly it would be far cheaper and easier to buy a quality aftermarket unit that would have better sound quality, better gps with free updates, and more features.
To give you a rough idea of what's entailed by upgrading using OEM parts:
Parts list and prices: https://www.infinitipartsdeal.com/parts ... m=280_A011