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.
Buy an upgrade with miles. If you have Sky Miles with Delta, you may use them to upgrade a coach ticket to first class. The number of miles needed varies, based on the length of the flight and the ticket purchased. Use your status to get an upgrade. If you are a Medallion member with Delta, you qualify for unlimited complimentary upgrades.