There are three (3) ways to delete contacts: delete a contact in the main screen, delete a contact in the list contacts screen, delete several contacts at the same time.
Delete contact in the main screen
Delete contact in the list contacts screen
Delete selected contacts in the list contacts screen
Note: You can manage contacts to select like temporarily omitting the contacts you do not want to delete using the the Omit button of the contact's line on the list. There is also the checkbox that you can mark and select only those that are marked.