Your car has a copper wire system, which makes upgrade very easy. I suggest you visit a decent car audio shop, tell them the features you want (there are modern units with Bluetooth for cell phones, with pop-up screens for GPS*navigation, and other capabilities). Nearly any good car audio shop can handle the installation for you.
Other than that, you could try online sellers such as Crutchfield, which sells not only the head unit and mounting kits, but also provides instructions for many types of cars.