Remove the faceplate of the Alpine head unit by pressing the release button on the corner of the unit. If your model has a flip-down faceplate, flip it down, then push the faceplate either to the left or right and gently pull back on it to remove it.
Remove the outer plastic ring surrounding the head unit by gently prying it off with the flat-head screwdriver.
Insert the removal keys into the guides in the mounting bracket on each side of the head unit.
Pull the unit out of the mounting bracket with the keys still inserted into the guides.