When body fat accumulates in the belly area, rolls form when you sit down or crunch up. If you repeat this movement often, fat lines will start forming in the area in-between where the rolls are. To get rid of fat lines, you need to attack not only the lines themselves, but also the fat that causes them.
Ergo, to get rid of fat lines you first need to shed the fat causing them. That means doing a lot of cardio exercises, possibly combined with weight training. Some trainers will tell you it can be done with weight training alone, but I recommend doing both with approx. 80% cardio and 20% weight training in order to shed the necessary fat while maintaining muscle tone. Trying to do it with only weight lifting will be more difficult if you lack motivation because you will tire easily due to low endurance.
Once you've shed the necessary fat then you can follow the steps below for getting rid of those ugly fat lines on your stomach.
Shed the necessary body fat until you have "six-pack abs". If you have difficulty performing this step I recommend hiring a personal trainer to get the necessary advice. Its cheaper than expensive surgery and you will feel better knowing you've done it the natural way.
Steps 2 and 3 are optional. They will speed up the reduction of fat lines, but they will disappear on their own if you do Steps 1, 4 and 5.
Treat fat lines as you would wrinkles or stretch marks. Apply moisturizing cream to them or massage with Vitamin E oil. Massage the chosen product into the skin and along the whole length of the lines. Repeat two or three times a day for as long as necessary. Creams and lotions that contain vitamin E will help soothe and regenerate the skin and with time will help get rid of stretch marks and fat lines, and even reduce the appearance of old scars.
For best results apply creams containing alpha-hydroxy acids (AHAs) to your stomach lines. You can find body lotions with AHAs in the ingredients list, but if the lines are deep and quite noticeable, you should try a face cream, as the concentration of AHAs will be higher. To use, simply apply over the lines and massage until the cream is absorbed. Creams containing AHAs can be combined with topical steroid creams to reduce inflammation of the skin and improve the appearance of stretch marks.
Remember for any of these steps to be effective you first need to lose the necessary fat and maintain your new weight once you've lost it.
Thus it is very important to maintain the same level of body fat otherwise the lines will keep happening (and returning) as long as your body fat is too high and you have rolling skin when you sit down. Maintain a healthy diet and continue to exercise regularly.
Perform abdominal crunches and ab exercises on a regular basis to tighten up the muscles in your stomach and firm up the skin above it.