It is hard to make recommendations without knowing what your current lifestyle is like. Nonetheless, I am going to second what some have already said - cut down on processed foods and try to incorporate as much "real food" into your daily life as possible. And incorporate some sort of exercise into your everyday life.
The key, in my opinion, is consistency. Do not try to suddenly go from eating 3 fast-food meals every day with no exercise to trying to go on a strict diet with 4 x sessions of HIIT a day. Will you lose weight? Yes, undoubtedly. Will it be sustainable? Not so much.
The key is to slowly start building healthy habits into your everyday life. So if you currently eat 3 meals of junk a day and down 6 cans of coke, for the next few weeks try to focus on adding in one wholesome meal per day and cut down your coke intake to 3 cans swapping the rest in favour of water for example. If you currently do no exercise, I would not jump straight into something as hardcore as HIIT - sometimes less is more. Maybe just try to work in a 30 minute walk 3-4 times per week at least for the first 2 weeks, then try increasing that to 60 minutes and/or more day/everyday. Walking may not be a calorie scorching workout but it is grossly underestimated as an aid to weight loss, particularly when combined with increasingly better eating habits. Once you can stick to that, you can up the level and maybe start exploring other forms of exercise - perhaps work in some body weight movements, or start exploring the wonderful world of weight lifting. Join a class, or even turn that run into a walk - the key is still consistency. Small incremental changes to your habits for the better over a longer period of time are bound to be more effective than drastic changes that will prove to be a psychological and physical struggle to stick to.
Best of luck!