You lose any fat by burning more calories than you ingest. There is no possible way to choose where you lose your fat. Once you start burning more calories than you eat (diet and exercise), you will lose fat - where that fat comes off of is not up to you. Fortunately, for a lot of people they notice a difference in their face/chin fairly quickly (this coming from personal experience and the experiences of people I know).

So start eating better and doing cardio and you will see a difference. But, it will take some time, so you have to be patient! :D