Actually, there's a lot more to it than Doug has posted. You would be mightly surprised at what Orbx fills up your FSX with.
If you
really want to uninstall FTX from your system, follow Doug's uninstall guide
here. I would also add that it is best to set everything back to default (Aero, Day/Night Lights back to Night) before beginning the uninstall.
Next, run separate searchs in your root FSX folder for: "Orbx", "FTX", "Avalon", "fx_HS_FSX_*" and "coff" (and/or "cof") (without the quotation marks

). Also be on the look out for any Australian ICAO textures, specifically "YMML" and "YPMQ" (that is unless you happen to have these airports already installed, of course).
There is Orbx/FTX detritus in: Effects and Effects/Texture; Sound; Weather/Themes; and Scenery/Global/Scenery, Scenery/Global/Texture and Scenery/World/Scenery. Adds up to nearly a Gb worth to manually delete.
Just an FYI.