To delete a contact in the Web Portal go to CRM > Contacts. Check the box next to the Contact you want to delete and then select Delete from the pop up menu at the bottom of the page.
Multiple contacts can be deleted at the same time. Once deleted, the Contact is permanently removed from the CRM. If you would like to keep their CRM information but 'archive' the Contact so that they are not active, you can also select Inactive from the list at the bottom instead.
Note: A contact cannot be deleted in the App, only via the Web Portal.