To modify your KLM flight ticket, log in to your KLM account, access "Manage My Booking," and input necessary details. Choose the "Change Flight" option, select new details, and review the KLM flight change policy, including potential fees and conditions. Confirm changes, make any required payments, and receive a confirmation email with the updated itinerary. Stay informed about KLM's latest policies and procedures by checking the airline's official website or contacting their customer service.