Edit Menu
Here's explanation of Edit Menu of Management Studio.
Delete
When a Custom Field Type, Data Definition*, Search Template, Style Sheet, Device or Depot is selected in the tree view, Delete enables you to delete the selected item.
* Unpublished Data Definitions can be deleted. Published Data Definitions can be deleted only if they have not been used to Index any data and all links to Search Templates, Retention Policies and Automated Indexing Watched Folders have been deleted.