To the best of my knowledge you can't edit contact owners in the property settings but would manage users via the "users & teams" settings. Here you can either deactivate a user or remove them from the account.
One important thing to keep in mind. Have you disconnected the Salesforce integration? If not, this might overwrite whatever changes you make in the owner assignments.
Hope that helps.
Frank
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If you're looking to remove salesforce users from the account, you would first need to remove them from any records and re-assign them to active HubSpot users and then you can clear them out by clicking remove salesforce owners on this page: https://app.hubspot.com/integrations-settings/typeyour accountnumberhere/installed/salesforce/cleanup.
I have removed them from all companies, contacts, deleted all tasks etc, did a full on clean, yet still cannot remove them from the dropdowns... I have raised a ticket a while back, and couldn't be bothered after being asked to follow normal steps after having explained that I already have.