Installing a new FS2004 disc to replace current one

I have REX2 installed (Real Environment 2) in my FS2004. I am installing a brand new FS2004 due to problems I have with the current installed version. My Q is: Do I need to uninstall REX and other programs (such as Ultimate Terrain) before installing the new version? Can I somehow transfer freeware aircraft? Any guidance will be much appreciated.