By not eating as much
By doing something as simple as cutting your portions by 10% at each meal you can train yourself to eat less and lose weight.
As you learn to eat less your stomach will actually shrink and you will become fuller sooner.
You can then reduce your portion size another 10%
By repeating this process you will be able to eat less, feel full and still lose weight.
You must ensure that you maintain an appropriate caloric intake for your weight, age and activity level however.