you cant modify or adjust existing objects, they are part of the map and are binarized hardcoded to the map.
to lay roads you will have to download a mod that makes the roads into objects which you can then lay down, however everyone will have to have this mod.
Roads are painted along polylines that are created in terrain builder.
If you want complete freedom, make an empty map with terrain builder (atlas guide to terrain building on armaholic). and then use x cam and what not to place all objects.
Due note this will be harder on the fps then making a normal map with the objects already on there.
