1 Leptin is a powerful and influential hormone produced by your fat cells. 2  It plays a key role in regulating energy intake and energy expenditure.
(Upgrades are not available on fares in the L, T, and U range, however, which are the most deeply discounted.) To calculate the price of an upgrade, Delta charges a dollar amount per 500 miles. $50: Up to 500 miles. $75: 501-1000 miles. $100: 1001-1500 miles.
The Delta system will automatically calculate the new cost of the flight, adding the change fees and any increase in fare. If the fare for your new flight is less than what you originally paid, the difference will apply to the change fees. Step 5. Pay for the new flight with a credit card.