Since there seems to be no solution yet in a previous post titled "Download Scenery Automatically" I decided to use "Add-ons / Install Downloaded Scenery" which takes you to the world graphical interface where you can download scenery in .ZIP files, After downloading the .ZIP file I went back to Flightgear and clicked the Next button to install the scenery file but the dialog box would not open .ZIP files, it wanted a .TAR, .GZ or .TGZ file to install. Seems like there is a problem here to fix?
As a solution I have been extracting the .ZIP files and manually copying the contents of the Objects and Terrain folders to the appropriate Flightgear folders. Just wondering if my solution is a correct procedure? (doing this everything seems to work fine)