Deleting forks of private repositories
While forks of private repositories are deleted when a collaborator is removed, the person will still retain any local clones of your repository.
Removing collaborator permissions from a person contributing to a repository
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En your GitHub Enterprise Server instance, vaya a la página principal del repositorio.
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Debajo del nombre del repositorio, haz clic en Configuración.

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In the left sidebar, click Collaborators & teams.

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Next to the collaborator you want to remove, click the X icon.
