Airmatic Problem on ML500 2006 Sport petrol

[fast cars]

My merc ML500 seems to be riding lower than usual and much firmer , approx 2 inches ?? the button inside does'nt make the rise like it use to , am no expert but can anyone advise before I make the dreaded trip to the MB dealer who will tell me I need a new car ? is there something like a reset button somewhere ?????

Many Thanks