Thanks, got that now but it doesn't let me change the infill - I thought it did but my memory failed me.
I found this uTube link yesterday, https://youtu.be/DGso6sAIXb0, which seems to describe the method to do what I want but I can't quite grasp how to get the separate .stl files of the hexagon example back together on the Cura build plate. When I open them they end up on edge and I can't see a way of putting them back together accurately.