The only way to lose weight permanently is to expel more calories than what you eat. The healthiest way of doing so is to stick to 2000 calories per day and do 30 minutes of exercise daily. A combination of strength training and aerobic exercise are very effective, the best of which are swimming and walking.
There is no miracle diet, and dieting alone will not get you the results you want as quickly or effectively. Just eat healthily, don't eat rubbish and exercise a lot.
I did this (and still do) for 3 months and I lost over a stone and a dress size! I also lost 2 further pounds over Christmas!