For those of you who want to delete several waypoints at a time I finally figured it out on Humminbird PC.
1 Download from fish finder to card
2. Load card to Humminbird pc
3 Put curser on 1st waypoint to be deleted
4 Hold shift key down and scroll down to last waypoint to delete
5 While still holding shift key down, right click within the shaded area
6 Select delete all
7 Follow screen instructions

IMPORTANT: This will delete all waypoints selected (shaded). Be sure you don't have a stray you want to keep listed in the group you pick. I use the google earth link within Humminbird PC to identify exactly where each waypoint is on the lake before I select it to be deleted. You can speed up the selection process by looking at same lat and lon and dates to be sure they're all in the group you're after. I got rid of about 300 doing this. Sure cleaned my screen up.

I have written this from memory, so be careful you don't mess up. I may have missed a step but this is close enough you can figure it out. Y'all probably already had it figured and I'm the one just now getting it.