I have a Nuvi 40 and loaded the OSM maps to my unit and it has created 96 disc image files under the directory named OSM generic routable (UK) As far as I can make out the live map file already on the unit is current.gpx under the GPX directory I assume I need to convert the OSM files to the current.gpx file How do I do this please

I have a Nuvi 40 and loaded the OSM maps to my unit and it has created 96 disc image files under the directory named OSM generic routable (UK) As far as I can make out the live map file already on the unit is current.gpx under the GPX directory I assume I need to convert the OSM files to the current.gpx file How do I do this please