First, navigate to the admin member directory via Admin > Members > Directory.

Then, filter or and select the users you'd like to delete using the checkboxes to the left of their names.

Select "Delete Members" from the "Actions" dropdown menu:

And type "Confirm" to confirm that you'd like to delete their accounts. This step cannot be reversed.

They will receive a notification by email to let them know that their account has been deleted.

If you want to bar a user from using your Switchboard because of bad behavior, consider banning them instead by scrolling to the right in the member directory and changing their role to banned.