Owners and admins manage memberships from the Members page.
Change a role
Open the member's row and pick the new role. The change applies immediately.
Remove a member
Removing a member ends their access to the organization. It does not disconnect the social accounts they connected: a social account belongs to the organization, and each member's authorization is a separate credential. If another member holds a valid authorization for the account, it keeps working. If the removed member held the only valid authorization, the account will need a reconnect by someone else.
Leave an organization
Any member can leave from the Members page. The same rule applies to accounts you connected: they stay with the organization, and someone else may need to reconnect them.