The key to successful, sustained weight loss is to make a lifestyle change - no fad diets, no crazy gimmicks - just good old fashioned healthy eating and exercise. You can try calorie counters such as CalorieKing (.com.au) to get an idea of what and how much you should be eating.
Keeping a food diary is an excellent way to keep yourself on track!
Start with increasing your incidental exercise - get off the bus a stop early, walk to the shops, take the stairs at work.. this all adds up! Then try for "sessions" that are 20-30 minutes long, 3 times per week. You should gradually increase this until you are doing at least 30 minutes daily.
You should aim to lose 0.5-1kg per week, but remember as you go your weight will fluctuate and sometimes you will lose less than this. The key is to keep sight of the big picture and stay on track - and your weight WILL go down!
best of luck