You can't get the sun's position or brightness to change in Preview using the Sun Height, Sun Heading, or Sun Brightness in the Sun Effect.
The Real Skies Effect is also in the Effect Stack and you already tried turning it off but to no avail.
1. Here's how to enable the Sun Effect settings:
1.1: Effects take precedence (control) if higher in the stack than another Effect.
Change the order of the Sun Effect in the Effect Stack so that it is above the Real Skies Effect.
1.2: The Real Skies Effect can be turned on again in Photo or Movie Mode, and you will be able to change the sun using the Sun Effect.
Real Skies are static real images and the sun is at a fixed height. If you change the Sun Height or Sun Heading via the Sun Effect whilst using a Real Skies Effect then you will have two suns in the sky. Avoid taking camera views (snapshots) with both suns showing.
2.1: Make sure that Real Skies are disabled in Build Mode before entering Photo Mode.
This will also prevent Real Skies from having precedence (control) over the Sun Effect. However, you now have no Real Sky in the Project.
Version 10 and newer (Real Skies in Build Mode).