Yes, you can upgrade a Lufthansa "Economy Light" fare, but your options are more restricted than with standard tickets. Because "Economy Light" is the most restrictive fare class (no checked bags, no refunds), you typically cannot use miles or vouchers to upgrade to Business Class. However, Lufthansa does allow "Light" passengers to purchase cash upgrades at a fixed price or to participate in their "Bid Upgrade" program. These offers usually become available after you've booked, either through the "My Bookings" section of the website or during the online check-in process (which opens 23 hours before departure). You might also be able to secure a last-minute upgrade at the airport check-in counter or gate if seats are available. Keep in mind that when you upgrade a "Light" fare, you will enjoy the Business Class cabin service and lounge access, but the original baggage rules of your Economy Light ticket may still apply.