Also remember that you should only lose about 1 pound a week. (Sorry, I don't know the conversion to metric.

) That sounds slow. But it adds up to 52 pounds in a year, which is a huge change. So, if you want to drop 50 pounds for "swimsuit season," you should start in June for the following year.
Also when you exercise do strength training as well as cardio, even if it is just isometric (like push ups or squats or sit ups.) Muscles require more energy so when you add muscle, you burn more calories even when you're just sitting.
Lastly, as you lose weight you hit a point where your body gets used to your new routine. So you need to add more exercise as you go until you reach your ideal weight. Once you reach that goal, you can't say "whew, I'm done!" Nope, you must stick to all the changes you make. So if you're walking an hour a day, you must continue. You can't go back to your old eating habbits. So when you make changes, make ones you can live with vs. doing ones you hate or can only do short-term.