Tap the "Edit" button and check the contact you want to delete. You can delete multiple contacts at once but the most you can delete at one time is limited to five for safety reasons (as of 1.3, you can remove this restriction in Settings / General). Please check the contacts you want to delete.
Tap the Delete button on the bottom right and confirm the action.
Contact has been removed. Please exit the edit mode by tapping the "Done" button.