Your stomach is a muscular organ and like any muscle it expands and contracts according to usage. So it stretches when it’s full and returns to it’s initial size when empty.
However, it’s not possible to permanently enlarge or reduce the size of your stomach by eating.
There are various types of weight loss surgery that can reduce the size of the stomach, but these methods of weight control require close consultation with your doctor.
For more on weight loss surgery to reduce stomach size, see: