yellowing leaves is an indication of under-watering ....water to saturation and place in at least 6 hours of direct sun
lightly press the caudex at the soil line....if the caudex collapses in on itself, root rot has occurred
a slightly spongy to hard caudex indicates a healthy adenium
pinch off all the leaves...(to get newer ones to take their place)... fertilize with an all purpose fertilzer (for green leaves)