It is quite simple to remove your Nissan radio. You will need t a flat-head screwdriver for prying the panels off the dash to Access the radio. Clarion radio removal keys are ideal for freeing the head unit from the mount.
Different car radio models require differently shaped removal keys.
For further help in removing your Nissan Clarion radio, please see this YouTube video
To find your Nissan serial number, you will need to remove the radio using radio release keys. Once the radio has been removed you will need to locate the radios label, which is on the top or side of the radios casing.