You can manage all of your contacts in your Address Book. You can create lists in your Address Book to use to send cards, and also access past lists.
Hover over your name at the top right corner of the screen and choose "Address Book" when the menu appears. From there, you will be able to add, remove, and edit contacts:
To add new contacts, click on the "Click to add a new contact" link (located under the Name header of your Address Book).
To remove contacts, check the boxes to the left of the contact name(s) and then click the "Delete" button (located above the Name header of your Address Book).
To edit a contact, click into the field you want to edit (Name, Email Address, or Mailing Address) to make your changes and click the red "Save" button to the right.
For more information about your Paperless Post Address Book, see here.