It's also important to take into consideration that running is not the best option for everyone. Cycling, swimming and rowing might be better options for some. The reason being that if you start running right off the bat, and your body is heavy, and perhaps you're not used to training, you very easily create more problems like chronic inflamation in the shin etc.
Walking uphill is also a great activity. But also watching the diet, avoiding sugary stuff is a good way to go about it.
You need to do cardio, cardio, and more cardio. Building muscle is great but if your six pack is under 2" of fat you can't see it without a scalpel.
When running max sure you keep your hear rate in the fat burning range. Initially you will want to use a heart rate monitor eventually you will just be able to feel when in the zone. Running too fast, too hard will spike your heart rate out of the zone. At that work level your body can't efficiently burn fat and still provide the needed energy so it switches to only burning blood sugar.
TL/DR version:
If you are trying to lose fat (as opposed to gain strength, definition, muscle mass, etc) you need to focus on cardio and keep your heart rate in the fat burning zone. Once you burn off enough fat switch to a more varied work out regiment.