OK, Gkup, as one old guy (71 this year) to another and at risk of over simplifying rumblerider's comment and insulting your intelligence, I'd like to lay this out the way I wish someone had done for me when I first started this stuff.
In order to read those .gpx files, you need to import them into a mapping software program. Like rumblerider, I use Garmin Basecamp. (This is where you can download the MAC version.
https://www8.garmin.com/support/download_details.jsp?id=4449) It's built to do a whole lot of things, but along with that flexibility and power comes a pretty steep learning curve. Basecamp allows you to not only view those files, but make changes to them as well. In addition, of course, you can also map out your own routes. If you want to modify or create routes, my suggestion would be to use a computer with a keyboard. An iPad may work as well, but I'm not familiar enough with them to know for sure.
When you decide you like a route and want to put it into your bike's GPS, export the file to a USB drive and follow the instructions in your bike's Infobrick (Sorry, Infotainment System) manual to upload it.
The most difficult part of all this is learning Basecamp. I'll be happy to help you any way I can. Rather than clog up this thread, feel free to PM me with any questions.