In Dungeon World, when you have enough XP to reach level 11, you can choose to change your class:
Changing classes means keeping your ability scores, race, HP, and whatever moves you and the GM agree are core to who your character is. You lose all other class moves, replacing them with the starting moves of your new class.
What does this mean for actual XP? Do you keep your level (10) and your XP (enough to reach level 11 the next time you rest), and just continue leveling from there on? I am not sure how that would work, because you would e.g. never again reach "level 11" and would thus never choose anything else from the list (which might be totally fine, keeping in mind the high stats and the amount of XP you need to level up from then on)?
The rules say nothing about it, so I assume that's really it, and nothing happens to your XP and level, but I might be missing something.