Simple way to move parts within Assy

[peet]

Hi,

I want to move a few parts in an assembly so that I can arrange them for a 3D printer. Specifically I have two parts, one is a mirrored version of the other part, and I want to rotate just one of these parts. Is there a correct way to do it? I have googled a lot on this, but nothing seems to work. This is such a simple thing to need to do, surely it is possible?

Any pointers much appreciated,

Thanks
Pete