Downloading previous tracks:

gpsbabel -i garmin -f usb: -o gpx -F file.gpx

Uploading routes

gpsbabel -r -i gpx -f file.gpx -o garmin -F usb:

Creating routes:

1. Draw route on Google Maps.
2. Use GMapToGPX to create a route.
3. Edit created route file to combine all <rte></rte> blocks.

Use GPSVisualizer to plot downloaded routes.