That small ring sits in a grove very near the end of the splines. It is an open ring like a "C". You do not need to open the differential to remove that ring. Sharply pull the half shaft/axle outward and the ring will collapse into the grove allowing you to continue pulling the half shaft all the way out of the differential housing.
Chrysler has discontinued that ring so hold onto it as you can reuse it if the new half shaft you purchase doesn't come with it.