Click with the Right mouse button on the map and a context menu provides access to a number of actions that can be performed. Most are dependent upon have an existing waypoint selected.  If no waypoint is currently selected, most of the options will be disabled.

Delete Selected - will, as you might expect, delete the selected waypoint from the route

Delete To Start - will delete all waypoints between the selected waypoint and the start of the route, the selected waypoint and the first waypoint in the route remain

Delete to End - will delete all waypoints between the selected waypoint and the end of the route, the selected waypoint and the last waypoint in the route remain

Start route here - Similar to delete to start, but this option also removes the first waypoint in the route leaving you with just the waypoints and distance to the destination, or as often referred to a Point- to-Port distance

Terminate route here - Similar to delete to end, but this option also removes the last waypoint in the route leaving you with just the waypoints from the first and thus a Port-To-Point distance