Just eat healthier and eat less, done. There's no magic science to it, just eat cleaner and don't be a pig, it's not as complicated as anyone makes it out to be.
Most important thing to do absolutely 100% is track every single thing you eat, at least for like a week. You will either be surprised at how much you are eating and start cutting back and being smarter about it, or the act of tracking it in the first place will prevent you from eating as poorly. It's win-win either way, success in most things is all about being organized and making things measurable.
Cardio is lame generally and I don't really recommend using it as a primary source of exercise. It will help you burn calories but it is impossible to out-exercise a bad diet. You can consume calories a hell of a lot easier and faster than you can burn them, so it is much easier to just not eat the extra calories in the first place. I recommend strength training over cardio for any form of exercise. A 45 minute strength workout will burn as many calories as a cardio session with the added benefit of actually building some muscle mass instead of just shrivelling your fat and muscle mass down into making you skinny but fat at the same time.
If you are eating to lose weight, you are not going to get huge and muscular anyways, but you can improve the muscle mass you already have and take advantage of some beginner gains. To get big you have to eat big, muscles are built in the kitchen so if you aren't giving your body enough raw materials to make the muscle out of (which you won't be because you will be dieting) then you do not have to fear becoming a big meat head, nothing to worry about there.
Just focus on good bang for your buck compound exercises if you start doing any weight training, stuff like barbell squats, deadlifts, bench press, overhead press, pullups (when you can do them) and some sort of rowing movement. They all burn lots of calories and work multiple large muscle groups.
