If all you're doing is the stereo head unit, then piece of cake. Crutchfield is great. They aren't the cheapest, asa you can find stuff for less if you shop around. But they have a great selection. They are almost always right on when it comes to what will fit and what won't. They miss the mark occasionally, as nobody's perfect. But their customer service is incredible. Plus, you will need the wiring harness adapters, as well as an enclosure for the new unit to fit in and fill up the extra space in the dash. This stuff, with very few exceptions, is free at Crutchfield when you buy a new unit from them.
They also send great instructions for how to remove your dash trim, as well as removal of the actual stereo. Install instructions are easy to follow, too.
So, go ahead. It's not hard. And an aftermarket unit will sound lots better. The only time you can't get much improvement is if you start with a Mercedez or Porsche or something that starts out with a high-end unit in the first place.
Now, if you're getting into speakers and other stuff, that's more involved. Lots of room for improvement there, even if you have the so-called Infinity system.
Hope this helps
SOLER