It is very easy. Eat more of the healthy stuff and none of the bad stuff. That means: Eat whole-grain bread, low-fat everything, drop the mayo, eat lots of fruits and vegetables, eat healthy meals (less pasta, more rice and potatoes), drink 2 litres of water per day. Eat fish.
Start with running as with everything else - slowly and not too far at first, then build up. If you're able to run 5K already then set up a training schedule of two 3K easy runs, 1 short 2K run, and a weekly long run (5K+).
The gradually increase, turning the 3K runs into one interval session and one hill running session, and the long run should grow every week. But every fourth week you kick back on everything and lower your mileage - ie a recovery week.
Eating healthy and regular exercise is really the only thing that will get you in shape!
Also remember that when you exercise you need more food. I'm 5'7" and weigh about the same as you, but I eat like a horse these days.
