NOTE... THIS MAY NOT BE UNDONE. THIS SHOULD ONLY BE DONE FOR CUSTOMER OR PROSPECTS YOU ARE SURE YOU DO NOT NEED IN THE SYSTEM.
Search the prospect or customer and go to their account data page as seen below.
Then go to the top right blue button labeled "Edit"
Then click on the red "Delete" button and this will delete that customer or prospect from the entire database. This will also delete any notes, estimates, bookings, etc. related to that customer or prospect and this may not be undone.