Stefan,
Many thanks for your quick response, it worked!
I think my error was in going via the main ribbon as opposed to the Design Explorer.
Also thanks to HaroldL for responding
I'm a relatively new Atom 3D user, so far I've been through the tutorial and and created some relatively simple assemblies with few problems.
However I find it difficult to get into an edit mode. For example I've completed a 2D sketch and used the Extrude function to create a part. I'd now...