Surgery usually. These days they do the op laparoscopically(keyhole) and it takes about an hour and 15 mins, depending on the skill of the surgeon.
You'll be left with 4 half inch scars on your upper abdomen where the ports of the instruments were placed.
It does depend on the severity of the hernia - some will respond to medication which supresses the production of excess acid. Your GP will refer you to the appropriate hospital for a barium swallow, so they can assess if your hernia needs surgery or not.