The brief answer to this is that an earthquake releases approximately 30 times more energy for each unit increase (by this I mean a whole number, such as an increase from 5 to 6) on the Richter Scale. As the link below tells us,
... an earthquake with a value of 7 releases 30 times the amount of energy as an earthquake measured at 6, while an earthquake of 8 would have 900 times the energy as one valued at 6.
Please note that this is not the same thing as the magnitude of an earthquake. With each unit increase on the Richter Scale, an earthquake's magnitude increases by 10 times. So, an earthquake that hits 6 on the Richter Scale has a magnitude 10 times greater than one that registers a 5. This is a different thing because it refers to the amount of movement that is caused by the earthquake rather than to the amount of energy that is released.