To delete a group of panels , please follow below steps:
1. Navigate to the Design Tool.
2. Expand the Panel Layout tab.
3. Highlight the "Multiselect" option.
4. Navigate to the desired array & hold and press the mouse on the panels you want to delete.
5. Once the desired panels are selected (in white dialogue box) , click on "Delete Panels now" on the right side of the screen.
6.Incase you do not want to delete the selected panel , you can "Unselect" the "Multiselect" option on your left & the selection will be thus off.
Here is a short reference video for the same: