Hi,Srikanth_Pandu.I hope this can help you if you uing the visual studio development environment.
firstly,change the dropdownlist control 1&2's attribute 'visiable'='false',
secondly,set the dropdownlist 1&2 attribute 'datasource',this may refer SQL connection or command,alse ADO.
thirdly,associate the ButtonCLick event with Dropdownlist display event,and in the ButtonClick reponse coding area,rebound the Dropdownlist.so the button click event will inspire the DropDownlist Update event.
PanZhang