The WRX is the high-performance version of the Subaru Impreza. Although it contains many upgrades over the standard model, much of the interior, including the radio, is the same. Removing the WRX's radio is the same as removing the radio in the basic Subaru Impreza. The radio-removal process is the same for the 2002, 2003 and 2004 model vehicle. Expect the procedure to last about 10 minutes.
Open the Subaru's bonnet and use your wrench to loosen the bolt around the black battery post. Grasp the cable attached to the post and pull it up to disconnect the negative battery cable.
Insert your trim tool into any of the corners of the radio panel. Pry outward gently to release the corner of the panel from the dash, and then move to a different corner. Repeat until the panel is disconnected. Set it to the side.
Remove the six Phillips screws from the radio. These screws become visible once you have removed the radio panel.
Slide the Subaru's factory radio out. On the back you'll find two connections. This is your antenna cable and your radio harness. Unplug both of them to separate the radio from the car.
Buy a trim tool from almost any automotive store, or online. If you don't have, or can't find, a trim tool, simply use a flathead screwdriver. Wrap the head with masking or duct tape to prevent the metal from scratching the plastic radio panel.