I'm sorry that this is such a ridiculous question. Maybe my brain isn't working today. I've looked over this forum and found references to rotating layers and levels, but always in the context of doing something more complex and clever. I've even found reference to the competition this year that seemed to suggest it was as easy as their being a 'rotate layer/level' option in the events window. I can't find this option! I've been faffing about with 'Set layer angle' but getting nowhere.
Is it because I only have the free version at the minute? Is it as simple as 'rotate layer'/'rotate level' being a glaringly obvious option in the full version?