When to change the game to Hard?

[Xirix]

I know for Witch Hunt you only need to change the difficulty to hard before the cutscene which leads to the boss fight.

But when do you need to change the game to hard for the achievement on this DLC? No spoilers please, I haven't played, I just want to know in advance when I need to change the difficulty.

[Steelstick]

I'll try to explain.
When you get to Dragonbone Wastes (I think it was called) you'll first have to fight some groups of enemies. After all those you'll have to walk for a short time and then you'll see a medium-sized open place and a gate you have to walk underneath.
It will autosave right before you arrive to that place, then you change difficulty.

*PS: if you ever played Awakening, you'll know where the end is (where you have to change)