Navigate to your 'Contacts' module on the left-hand side of your admin page.
From your contact table, you can select the contacts you would like to delete by selecting the tick box on the left side of the contact record, then select the more options icon.
The following overlay will appear:
Once deleted, contacts will be archived for a further 30 days then permanently deleted. This will anonymise all historical transactions related to this contact. After this point, this action can't be reversed.
Contacts who are administrators, active members or main contacts will not be deleted.