It is only possible to delete scopes which are empty. As soon as there is a model in the substructure you won't be able to delete the scope. So you first need to delete all models of the scope you want to delete. Now you may think this is time-consuming if you want to delete for example 100 models, but rest assured it is not. Below you will find a method to first delete the models in the scopes and then the scope itself.
First, you have to Expand all scopes in the navigation and then you collapse all scopes except the one you want to delete. Now you have all sub-scopes of that scope expanded but all others are collapsed. This is important for the next step otherwise you could delete models, you don't want to delete, by accident.
After that, you can select all models which are displayed with Ctrl+A, and now only the models from the expanded scopes are selected (that is the reason why we first needed to expand all and then collapse all scopes except the one you want to delete). With right-clicking one of the selected models, you can check the number of the selected models.
Now you either delete the models directly from the context menu (right-click at a model) or you press SHIFT+Del (with that shortcut you delete the models directly which means they are not just moved to the Recycle bin).
Finally, the scope and substructure are empty and you can delete the scope in the Scope explorer.
