This page of our guide to Wolcen Lords of Mayhem has information on how to change the difficulty level and how to unlock the veteran expeditions level.
How do I choose a difficulty level?
In Wolcen Lords of Mayhem, you don't choose the difficulty level at the beginning of the game.
You can, however, change it at any time in the game's starting menu. All you have to do is enter the options and choose the difficulty.
How do I unlock the veteran expeditions level?
To unlock veteran expeditions, you must complete the entire storyline at adept level. Other expedition levels will be available when you finish the game at the veteran level.