I lost 30 kgs and went from 120 kg to 90 kg. I hope I am qualified to answer. Before the answer, here are my actual before and after photographs. I achieved this without gym.
My routine to achieve this -
  1. Get up at 6 o clock and run. Initially in first 2 months, you should not run, just walk, because you will neither have the stamina to run, you might fall unconscious, nor can your legs take that much weight. After 2 months, I lost around 10 kgs just by walking and the diet written below and only then I started to run. I currently run at 10km/hour speed for 10 minutes straight without any break. But it took time to develop this speed and stamina. You will have to give that time.
  2. Diet - Anything that is cooked is spoiled. Anything that is raw or boiled is good. Anything high glycemic ( search on net ) is bad, low glycemic is good. Know and write down the glycemic index of all what you eat. Rice, potato and sugar have very very high glycemic index, avoid them at all costs. Once a week is fine. I simply don’t eat them.
  3. Vegetables generally have low glycemic index, especially the green ones. Go ahead, eat then as much as you like - but boiled, and steamed not cooked. By doing this, you will deprive your body of outside fat, and your body will start using the fat it stored inside yourself - exactly for these times. We evolved from primates and this phenomenon of storing access fat was used in hibernation.
  4. Don’t be hungry. Its a misconception that eating low is beneficial. No it is not. it will make you deficient in vitamins and protein which will adversely affect your body. Eat as much as you like, just eat low fat and low glycemic. But do eat, by all means.
  5. Be patient. Body takes time to adjust and give result. It can take weeks before you loose first 5 kgs, but it will happen. Weight gain is 100% reversible. But give it time. It will work. Its science. Just don’t give up in between. 90% people give up in just days because they expect overnight results. The rest 10% actually get results.
  6. Do good exercise, don’t show off. Don’t worry about the song you play while workout or the branded t shirt and shoes. They don’t make you in shape, your exercise does. I have seen people doing shopping of 10,000 rs before joining gym then not going to gym after 2 days. Tshirts and branded shoes don’t make you thin, workout does. I wear a simple 150 Rs cotton tshirt while running . You exercise for yourself, not for the world. Don’t post Instagram of Facebook posts for this. Work hard in silence. You will have enough to post when you are in good shape.
  7. Don’t give up, never give up.