In order to drop Israeli citizenship you must have another one, live outside of Israel for at least two years and request a form from the consulate, called VITUR AL EZRAHUT. It takes about two years to get it processed. It used to be a 7 days affair, until in the mid 80, when the goverment inssist on Mas Nesiot, people were dropping their citizenship by the hundreds. If you are a jew, you can always get it back - by the law of return.