Install GPX with Start 50 - tomtom Home.

All depends upon the style of your *.gpx file (there are 3). If you have built a *.gpx that uses either <wpt> or <rte> (NOT <trk>), then converting this to the TomTom itinerary file (.itn) is easy, and you place such files directly into the "Itn" folder on your Start 50 using your PC -- Home isn't needed for this.

You can look at your *.gpx file with any text editor to see which of the three constructions that it uses, then use a tool like TYRE to convert the *.gpx to *.itn for your TomTom. That tool can be found here >> http://www.tyretotravel.com/download-tyre/
Just load a waypoint (<wpt>) or route (<rte>) style *.gpx into TYRE and then export as a TomTom *.itn file, and with your device plugged in, move the *.itn file to the "itn" folder on your 50.

Then you can execute your route as an "Itinerary" on your 50.