If you are using the Delete Section feature to delete a sectiom from the end of the route you need to make sure that the red marker is right at the very end of the route (most easily done with the slider) before confirming the delete. You can tell it's at the end as the whole of the section to be deleted wil be whited out with no dashed line to indicate a replacement section.
Alternatively, you can use the Delete Homestetch feature, which is easier for deleting sections from the start or end of the route, as you simply drag the start or ened back alomg the route.
How do I delete the WHOLE ROUTE?
There are instructions for deleting a saved route in this topic: How to Delete a Route
how not to show distance mark ?
How do I delete an un-named, un-saved route - just clear the page! Undo takes for ever.
I see how it's done.