I have been excercising for a while to lose wait now and eventually I've lost some weights. However the fat around my belly hasn't been burned. Please advice me what to do.
Do cardio 3-5 days a week, also make sure you get a good sweat out of it.
Ab exercises will help firm up the muscles, which will make it more apparent when you do end up losing the fat. Strengthening you're core is always a good thing, and it tends to make you feel better about yourself which leads to exercise and eating healthy being easier.
And ofcourse the obvious eat less / don't eat foods heavy in fat and sugar.
There really is no easy way to do it, when losing weight belly fat is some of the last to go.
Also everything this guy said is pretty accurate:
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 (or any form of cadio) make 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. So instead you will want to run slower/easier for longer periods of time. If you are going to run remember running is destructive to the body (literally components are damaged, degraded) so you need off days. Initially I would say run no more than 3 days a week and eventually you can bump that up to 4 or 5.
TL/DR version:
If your goal is to lose fat you need to focus on cardioand keep your heart rate in the fat burning zone. Once you burn off enough fat switch to a more varied work out regiment.