Yes you can, unfortunatley it cannot be swapped as easily as most vehicles allow. The head unit in your car also controls security, door chimes, and on some models the low fuel, tire pressure, etc systems.
This is a royal pain in the you know what. To preserve system functionality the original headunit must be moved to the trunk of the car with part of the wiring harness still attached. You can find adapters that seperate out the right wiring all over the net for around $30. Once the unit is moved to the trunk (in a custom made box hopefully) you can go about installing an aftermarket head unit in the dash. You'll need another converter to make matching new head unit wires up to the existing harness easy....another $20 or so. You will also need an install kit for your car...this is a plastic case that allows an aftermarket headunit to fit and look proper in the existing space.
Now, with that said....changing the head unit by itself isn't going to do much. You may notice a minor improvement in sound quality but nothing significant. The factory speakers in your car are paper cone/extremely cheap...to get any real gain in sound quality you will need to swap the head unit and the speakers.
If you're really going all out you can consider an amplifier/sub for the trunk and another amplifier to power the interior speakers. It's just a matter of how much time and money you want to invest!
Hope this helps!