Please don't take this the wrong way, I don't mean this to sound condescending, but it's a very simple equation = expend more calories (energy) than you eat.
Get to know your portions:
Portion of protein - palm of your hand
Portion of carbs - one handful
Portion of veg - double cupped handful
Try a calorie tracker to get yourself in the habit, they do help but it's easy to become obsessive with them. Losing excess weight should be part of a long term healthy lifestyle. Don't be fooled by gimmick diets, they are conjured up by marketing teams to sell something and will usually end up with your weight yo-yoing, which is very unhealthy. The weightloss industry is worth billions worldwide!
And please, consider doing some excercise. Just start with going out for a walk a couple of times a week, then build from there. You'll be surprised how much you start to enjoy it!