beamng world editor problem

i want to delete the railing to get an nice crash but it only comes up as forrest and when i delete that it deletes all of the forrest on the map. so i need help

 

Click the icon at the top that looks like a leaf, that's the forest. Then look on the left for the brush tools. Look for the delete/remove tool and paint over the items you want to remove, or use the select tool and click on stuff to highlight the item and press delete.