Dudley,
Just to make sure you get what I am saying. Save your My log. Uninstall Airnav and re-install to c:\Airnav, instead of c:\programfiles\ where it will suggest. You may need to download and install the drivers again.
Down load and install the update, it will only go to program files, copy across the new Navdata db3 file from the default location to your new data location on c:\airnav replacing the Navdata db3 thats there and the move your mylog into the same location replacing the one that is there as well.
Hope you get all that
Alan