You can close any collection you belong to, even if you didn't create it. Closing a collection prevents people from adding new messages to it and removes it from people's list of collections.
To close a collection, click , then select Close Collection.
To reopen a collection, from the navigation menu, select Collections. In the Show menu, select Closed, then open the collection. Click , then select Reopen Collection
You can discard a collection only if you're the sole member. A discarded collection is removed from all lists, including other collections and Social Objects it's related to.
To discard a collection, click , then select Discard Collection.
For more information, see How do I close, reopen, or discard an item?