Please, do not try a green tea diet. Drinking green tea is great, but it can not be the one and all.
Mix it with exercise and healthy diet - yes you heard this thousand times before but it is true.
To burn fat and stay thin long-term you have to build new habits - that includes eating and exercise habits - into your life. Unfortunately it is not as easy as drinking a great liquid for a number of days and weeks and then problem is solved...it is a process.