Hello klopfer,
an administrator can modify permissions for any workspace through the "workspaces" icon in the administration panel.
You should find the workspace in the alphabetical listing and click edit. After this, you should click on 'edit permissions' and just click save (administrator is checked as default, so you will be given permissions over the workspace).
To remove or modify these permissions, you should go to the administrations panel, "users" icon, and select change permissions.
We know this is not user-friendly nowadays, and aim to restructure it some time soon.
Thanks,
Marcos