To remove a repository from the Repository Manager, right-click on the repository in the Repository List panel (LHS) and select Remove.
If the Syndeia client is using Syndeia Cloud (Cloud Mode), then a repository can only be removed by users if:
(1) there are no inter-model relations created to artifacts/containers in those repositories.
(2) they have the permission to delete a repository
Generally, repositories should and can only be deleted by Syndeia Cloud admins. Refer to this section - Repository deletion.