That wasn't the problem. I could activate the cam file, no problem, just couldn't select the specific cam I wanted until I found the help screen I've posted above.
Still no clear instruction of how to edit the Z axis. But at least now I know how to select the camera I want to discover the cam name and then edit the Z axis in notepad.
Incidentally, seems counter intuitive but to raise the height of a camera you increase the NEGATIVE value.
So changing the Z axs value from -2.0 to -1.0 will lower the cam's height whilst changing the Z value from -2.0 to -3.0 will raise the cam's height.