Same question here! I like the "Suggest a Ride" feature, but sometimes I want to edit it before downloading a GPX file. It's easy to make the route longer but I cannot find any way to make it shorter! Can someone please explain how to delete waypoints (or "via points") or state that it's not possible?

You can remove waypoints if you click on them (or just push if on touchscreen). You should get a popup like this:

From there, just click Remove via and it'll reroute accordingly :-)