Start slowly.
Don't eat fastfood, ready meals or anything like that.
Don't drink calories - switch to non-sugary drinks. No coke, no juice, no smoothies... Limit the amount of milk you drink.
Before eating, have two large glasses of water - add a few drops of lemon if you like.
Have vegetables at every meal - in this case, veggie which have been frozen from fresh are perfectly fine.
Cut your intake of carbohydrates in half. Carbohydrates are mainly found in pasta, potatoes, rice, bread and fruit.
Go for a walk every day. Does not have to be a long one - just feel that you are doing something. Start with 10 minutes.
If you struggle to do this, get some resistance bands and look up exercises on the internet that fit your fitness level.
If you have to have comfort food, dark chocolate and a handful of almonds can normally help.
If you feel very hungry at the start, try soups that are blended. Cauliflower soup, blended veg soup, tomato soup - these will make your stomach empty less fast, so you feel more full for the amount of calories you take in.
Don't be too afraid of fat. It is often the body's response to carbohydrates which will trigger insulin which will store fat that is the problem.
Join a page where you can track your food and exercise. It will allow you to spot things you can alter later. It can also be a great motivator. It saves most of the calorie counting...
Know that it will take a while. Have multiple targets. Waist measurement. Fitness level. BMI/weight. How you feel. The more ways you find of measuring progress, the more likely you are to get a reward = success often. And you need that for a long stint of weight loss.
Reward yourself when you succeed in reaching a main goal - 400 lbs, 375... Lost 4 inches off your waist. Don't make the reward a food item, though. Get a gadget you want, a new CD, a book, some clothes (you will need them)...
Good luck.