Look, you've been getting a lot of conflicting advice on this forum lately, so I figured I'd jump in and offer my own 🙂
First off—and you probably already realize this—losing weight isn't actually the hard part. Staying at that lower weight? That’s where people struggle. About ten years ago, I dropped 30 pounds and actually kept it off, so I know what I'm talking about.
It’s a vicious cycle when you lose weight, gain it back, lose it again... just spinning your wheels forever. People call it yo-yo dieting. It’s frustrating because every single time you try to drop the weight, it gets harder. Your body learns. It starts to "understand" that there are periods of feast and famine. So, every time you go on a diet (the famine), your body tries to be efficient by burning as few calories as possible. That makes every subsequent diet a steeper uphill battle.
Based on where you're at right now—both your current weight and how you're talking about it—it's clear that managing your weight is going to be an ongoing struggle for you. You'll always have to stay mindful of the scale. But hey, that’s just something you have to accept and build your life around. Diets aren't going to be your long-term fix. I know it sounds like a cliché, but you really have to change your entire lifestyle. And please, don't try to drop 20 or 30 pounds in a single month. The chances of you keeping that off are basically zero. I know when you're 15, a month feels like an eternity, but you didn't hit 275 pounds in just a couple of months. It’s going to take time to shed it.
My advice? Set a set of rules for yourself. Rules you will follow religiously. Always.
1. A classic move is to simply stop eating after 6 PM. Just stop. Period.
2. Second, find some kind of aerobic exercise that you actually enjoy. Sure, at 275 pounds, running might feel pretty brutal, but once you get down to maybe 220 or 230, you might find your stride. Whatever you pick, it has to be something you like, otherwise you'll just quit. It has to become a way of life. Plus, aerobic training is great because it keeps your metabolism revved up even after you're done. Check out this running FAQ; it’s solid and covers principles you can apply to any cardio:
http://www.faqs.org/faqs/running-faq/beginners/part1/3. Walk. You won't lose massive amounts of weight just from walking, but if you do it daily—listening to music, chatting with someone, or just clearing your head—you're looking at maybe 200-300 calories burned a day. When you multiply that by 30 days or 365 days, it adds up to something significant. Also, since you're carrying extra weight right now, you're using more energy just to move. An hour of walking might burn you closer to 400 calories.
As for specific diets or workout routines, the internet is overflowing with info, and people in these threads have already pointed you in the right direction. But honestly? I think persistence and moderation are what matter most. Extreme diets or insane workouts will just burn you out, and then you'll give up. Then you're right back at 275. You have to be steady. Small steps, but constant ones. Don't quit.
Good luck.