How do I make nav/landing lights bigger?

Hi there, How do I increase the size of nav/landing lights? My nav lights on the wing tips are tiiiiny and my nose landing lights aren't any better. I tried editing fx_2.bmp (in phoyoshop) which most nav lights seem to use but I couldn't figure it out. Do I changes the bmp? is it in the .fx file?? Any help would be appreciated!Torsten