Generally, Delta Air Lines does not allow passengers holding a Basic Economy (E class) ticket to purchase or use miles for an upgrade to Comfort Plus, First Class, or Delta One. Basic Economy is designed as a "value" fare with significant restrictions; it does not allow for seat assignments until after check-in and is typically non-changeable and non-refundable. According to Delta's strict fare rules, these tickets are also ineligible for "Paid Upgrades" through the Fly Delta app or website, and Medallion members are not eligible for complimentary upgrades regardless of their status level. The only way to "upgrade" from a Basic Economy ticket is often to cancel the flight (subject to a cancellation fee which results in an eCredit) and then rebook a Main Cabin ticket, which would then be eligible for further upgrades. Always review the "Restricted" notice during the booking process, as Delta makes it very clear that Basic Economy is a "no-frills" experience intended for those who prioritize the lowest price over flexibility and seat comfort.