If you haven't sent out any digital stationery or no one has RSVP'd on your site yet, you can bulk delete or edit your guests using the bulk edit tool found in your guest list. 

You can learn more about bulk editing guests here.

If you have duplicate guests that you mistakenly imported, you may need to delete each guest individually to make sure you aren't deleting the guest entry with their RSVP responses and contact details. 

Learn how to delete, edit, and manually add guests here.