The mirror glass is symetrical, so the same may be used on both sides, although different galsses are available. Tilt a glass to face upward,and look into the gap between the glass and its housing. You should be able to see a black plastic spike pointing straight down, in the middle. If not, tilt the mirror down and repeat.
Press the spike with a screwdriver to one side, which rotates a ring on the back of the glass, in turn releasing the glass assembly. Take it easy-you don't want to break the spike off-if it doesn't move with moderate pressure, try the other direction. It only moves a few mm
The spike on the other side of the car may be in the opposite position.