Getting to the Stock Head Unit is pretty easy. Should take about 20 minutes to remove and replace.
To remove Stock HU...
Apply Park Brake.
Remove little plastic cover on top of the steering column.
Use a flathead screwdriver to push in slot under cover to move gear lever all the ways down.
Starting with the bottom left corner of the dash trim, pry the dash off to release about a dozen clips.
Unplug 5 - 8 connectors behind the dash trip, number varies with model (sunroof, fog lights etc).
Remove HU with phillips screwdriver to remove 5 bolts.
Reverse above order to replace HU.