From the error message, it appears that you are trying to upload the theme as a plugin. Make sure to upload it as a theme (under Appearance > Themes > Add New).
I highly recommend checking out this excellent how-to by @WPExplorer if you need further help installing:
Seems to me you are trying to install the theme here:
Plugins => Add New
where you should to install from here (Installable WP file only):
Appearance => Themes => Add New