Hi Mara,
For sections that definitely don't exist any longer, you can select the segment by right-clicking nearby on the map surface, click on "Find near this point", then on Edit and select Delete. You'll be prompted for the reason for the deletion: select "Feature does not exist".
For College St I would recommend converting it to a trail so that it can be used in walking/biking directions. To do this, select the segment using the same method as above, but select "Convert to trail" from the Edit dropdown.
Hope that helps. Let us know if you have further questions.
Andres