Delete Change Log for 1 contact
It depends on what you are trying to do.
If you want the complete removal of the contact, together with related entities (like address, activities, event participations etc.), then permanently deleting the contact will delete all the associated entities.
If you just want to remove the change log for that 1 contact without deleting the contact, you can run a simple SQL query to delete it. For a contact with the contact id 57 you would run this:
DELETE FROM `civicrm_log` WHERE entity_table LIKE 'civicrm_contact' and entity_id = 57

Beware, if you used something like Drupal webforms, then the data can still be there in the webform submissions, even though you deleted it form CiviCRM.