Copy the gui folder from the image of your choice in the archive (zip) into the res_mods/x.x.x folder of the game. Where x.x.x is the current game version.
Sound will ONLY work with 0.9.16 and later
Copy the audioww folder into the res_mods/x.x.x folder of the game. Where x.x.x is the current game version. Then select the sound you deisre. To test just double-click on the sound, your default audio player should play it. Then delete sixthSense.mp3 and rename the file you select as sixthSense.mp3. The default sound is Unit_Detected.
In the game Menu->Settings->Sound select "User Sound" then Apply