How do I undo in RawTherapee?

I can see, that RawTherapee creates kind of a history of edits, but how do I undo a step back?

Just click on the last step in the history you want to keep and continue editing from there. All previously following steps will then be replaced by your new action.

Or use Ctrl+Z to go back in the history stack, Shift+Ctrl+Z to go forward.