How do I install the Elektro theme on the StartLogic hosting site ?
I clicked on themes in the journal section within php Nuke, but the Elektro theme was not listed in the drop down menu.
Also, the Admin for the Forum section of phpNuke does not have any style options at all, it's the subsilver default only.

Any advice would be very much appreciated.

Nuke Admin> Preferences> "Default theme for your site"

When installing a new theme, it's a good idea to set it in "your account" first to test it out. Then if you decide you want it to be the default theme for everybody, set it in the admin section as mentioned above.