Downloaded and expanded .zip. Reading the install HTML page. It says there's 3 folders which I have. But, they don't match.
I have plugins, root, themes.

Instructions says I should have plugins, zenpage-default and root.

Do I proceed?

zenpage-default should be in the themes folder. Just move that to the themes folder in your zenphoto.

Thanks. I see the written info following says "themes" folder so must have been minor error.

Well, thanks for finding the typo..:-)