There are some crash diets out there that hhave been proven and work when trying to lose weight quickly. But they ALL have negative effects on your health, so i would not recommend any of them!
Introduce changes graduallySmall changes can make a big difference. One extra biscuit a week can lead you to gain 5lb a year – cut that biscuit out of your diet and you'll lose the same amount.
You're also more likely to stick to, say, swapping full-fat milk for semi-skimmed or making time for breakfast each morning than a diet that sets rules for all foods.
You should think of weight loss in terms of permanently changing your eating habits. While weight-loss goals are usually set in term of weeks, the end game is to sustain these changes over months and years, ie lifestyle change for life.
As im sure you you can guess this simple process does work, but it could be a little while before you see any changes, however it does take the risk out of your "lifestyle changes". Just dont be disheartened.