To manage your team, go to Organization settings - Team section.
To be able to manage your team, you need to have either Owner or Manager role in the Organization.
To remove users from your team completely, click on the team member's name and then the Remove button at the bottom. This will remove the given user from all social profiles that they had access to and they won't be able to manage the profiles anymore.
If you want to remove access for a given user only from some social profiles, but not all of them, make sure such user has a Member role first - you cannot customize social profile access/roles for Managers. Then simply enable/disable access to the given social profile(s) by toggling on/off the toggle button(s).