Make a lifestyle change. Any "diet" you go on may help you lose some weight but you'll tend to gain it back if you go back to your previous ways. Unhealthy diets also can cause weight loss of tissue other than fat (such as muscle, especially if your calorie intake is too low). Use a site like freedieting.com to determine about what your calorie intake should be (look for the Daily Calorie Needs calculator link on the left side of their home page). You can lose UP TO 3 lbs per week in a healthy manner, but 1 - 2 lbs is much more doable and easier to maintain long term.
Eat a healthy well-balanced diet at least 80% of the time...keep junk food, fast food, sweets, sodas, etc to a bare minimum (the occasional treat if you feel the need). Avoid as much processed food as you can. Focus on lean protein, fruits and veggies, complex carbs, healthy and healthy fats. Keep your calories at a healthy level when working to lose fat ...add to that a lot of water, and cardio exercise (shoot for at least 1 hr/day, at least 5 days a week) and you'll be on your way! If you don't have an exercise program you want to use, youtube has TONS of fitness videos you can check out, not to mention just getting outdoors and going for a walk, run, or bike ride.
When you reach your goal, simply modify your calorie intake and/or exercise to allow you to maintain your weight instead of continuing to lose.
How to lose weight has been asked/answered here in various ways, literally THOUSANDS of times. That's why there's a search feature at the top of the page. The should be no need for anyone to type another answer to that question, because all the information is already available, if you just do a quick search.