KLM provides various ways for passengers to upgrade their seats, which is quite straightforward. Passengers can request the upgrade during the booking process or after the booking by visiting the official website of KLM, by speaking to a live person at customer service, or at the check-in. However, the Upgrade to Business Class KLM is only offered when there is a seat remaining in that particular cabin. To learn more details on this, visit the official website of KLM or check out the blog linked above.