Start doing some weight training, replace food in your cupboards with healthy stuff, lots of beans, nuts, fresh fruit, veg, fish and lean meats, tasty sauces and spices, learn to cook properly instead of living off of takeaways, go shopping for real whole foods at your local greengrocers (eg. I bought 8 passion fruits today they taste amazing and are better than eating toffees and are great for you too).
Reward yourself once per week with a day of whatever you fancy, but eat it in moderation, you have been gifted with a metabolism which can process vast quantities of food, use it, don't abuse it, and you can probably become extremely healthy quite easily with minimal effort.
Get regular moderate intensity exercise that isn't just treadmill stuff, try walking, hiking, cycling if you have a bike, tennis/badminton/squash, climbing, yoga, trick is to give yourself a more healthy lifestyle that's fun and enjoyable, get out and meet other people who are active or in same situation as yourself rather than punishing yourself for the mess you got yourself into.
For more advanced cheating / body hacking you can also try taking 1tsp bentonite clay or 1-2 tablets of chitosan after large meals, that will absorb some of the fat you ingest. Try some supplements like a multivit, probiotics, vit d3, mag/zinc, omega3s to plug the gaps in your diet too. Try taking cold showers/baths on a regular basis, these man you up considerably and also forces your body to switch fat from storage to heat burning mode. You could also try fasting (ie. not eating for 12-24hrs) 1-2 per week, then reward yourself with a feast of healthy meals you learned the recipe for whilst you starved
Priority should be increase your mental wellbeing, getting healthier, boosting energy levels, enjoy life more, losing weight will just be a nice bonus.
Good luck man.
