There's a real risk of frustration from lack of weight loss if you're counting on the exercise alone to help you lose weight. You asked 'where do I start?' and my suggestion is to do the cardio if you want ( 30 minutes 4 days a week is more than enough), and I would add 30 minutes of resistance exercise 2-3 days a week to build muscle and preserve it during wt loss (you can lose as much as 35% of your weight from muscle which slows down metabolism), but you must focus on your calorie intake if you want to lose significant weight.
Since you sound serious I suggest the following:
1. Continue with exercise. It burns calories, it will keep you fit and strong, and it's the best predictor of keeping your weight off.
2. For the next week write down every single morsel of food you eat, and every ounce of beverage with calories you drink. Estimate the portion sizes as accurately as possible, and weigh and measure everything. Get a food scale and measuring cup to do it accurately.
3. Then go to the following site to figure out how many calories you are consuming
http://www.webmd.com/diet/healthtool-food-calorie-counter 4. Then to this site to estimate how many calories you burn all day (called the 24-hour energy expenditure (24-hrEE)
www.webmd.com/diet/healthtool-fitness-calorie-counter
5. Then here
http://www.webmd.com/diet/healthtool-metabolism-calculator to estimate your metabolic rate. Use the "Inactive" activity level for an additional cushion for underestimation of calorie intake.
Once you know your 24-hrEE, and how many calories you consume, you can modify your intake accordingly, and/or increase exercise, so that you burn more than you consume. For instance, if you consume 2000 calories in a day and burn 1500, then you know you have to either cut back on your calories and/or increase your exercise to turn it around.
If all of this is too confusing, then just do #1 and write down everything you eat. If you do just that you'll lose weight. Feel free to post back if you have questions.
You can post your diet-related questions to the Diet Community:
http://exchanges.webmd.com/diet-exchangeFinally, weight loss can be difficult on your own. WebMD has excellent resources to help people lose weight. You can get all the support and expert guidance on your diet that you need by checking out the Diet Community and the Weight Loss Clubs. The support and guidance will be extremely helpful to you.
Here you can select one of the Diet Clubs based on how much weight you want to lose.
http://exchanges.webmd.com/dieting-club-10-25-lbs-exchangehttp://exchanges.webmd.com/dieting-club-25-50-lbs-exchangehttp://exchanges.webmd.com/dieting-club-50-100-lbs-exchangehttp://exchanges.webmd.com/dieting-club-100-lbs-exchange You'll find everything you need to lose weight on these sites. And of course, feel free to post back here if you have more questions.
Take care, Rich