You can probably change from an endomorph to an mesomorph with regular exercise. Focus on improving. I recommend biking, push-ups, and weight lifting. For your diet just try to eat healthy food. If you exercise regularly then you will probably crave healthy food and want to drink more water. Having a more active lifestyle is a good way to reduce junk food cravings. You may need to eat more food to lose fat.
Taking a day or two off a week can help you lose fat and build muscle. Your muscles need to recover. I gained a lot of leg muscle by biking one day a week. You don't need to work out every day and you should not be on a strict diet. Focus on doing things that are good for you. Don't just workout to build muscle. Start some new hobbies like cycling and kayaking.