You might try exporting ALL of your waypoints and route to a SD card.
Upload them into Humminbird PC (free PC program from Hummingbird Support Website).
Edit your waypoint and route list in HB PC. Much easier than in the head unit.
Delete ALL your waypoints and routes from the head unit.
Download the modified list back into the SD card.
Import the the new modified list into the cleaned head unit.
May sound more complicated than it really is. Once you have done the process once, it can go pretty quickly.
The upside of HB PC is that you can do it from the comfort of your home and you can look at the waypoints in Google Earth to make sure they are the ones you want to delete.